Malaria is one of the most challenging problems in the tropical parts of the world, causing about 1.5 to 2.7 million deaths annually. Ninety percent of these deaths occur in Sub-Saharan Africa and 5% of children die from the disease before reaching 5 years. Malaria isresponsible globally for 500 million clinical cases and represents a public health problem for 2.4 billion people. People living in lowland areas, where malaria is common, acquire some degree of immunity against it due to frequent exposure. In the highland areas, however, people don’t have immunity against the disease. If malaria is introduced to such a highland area, people are at a higher risk of getting serious malaria and epidemics (highland malaria). The spread of chloroquine-resistant Plasmodium falciparum throughout the African continent has stimulated a search for alternative technologies that may play a role in the malaria control strategy. Insecticide treated nets have been clearly proven to reduce transmission, morbidity and mortality rates of malaria in many high-endemic malaria countries. Studies have shown that use and re-treatment of bed nets is relatively uncommon in many communities, but there is limited information about the reasons behind this, especially in areas where malaria has recently been introduced.The objective of this study is to describe factors influencing the use and re-impregnation of bed nets in an area where malaria has recently been introduced. This was a cross-sectional study, conducted in three highland villages in Tanzania from September to November 2001. The study consisted of two methods. First, a quantitative household survey was conducted; thereafter 12 informants took part in a qualitative inquiry using semi-structured interviews. The quantitative survey used a two-stage stratified sampling procedure in which 303 households - 100 without bed nets all, 100 with untreatedbed nets and 103 with treated bed nets - were identified, and the heads of households interviewed. A survey team consisting of 3 persons conducted the interviews. A pre-tested questionnaire was used to interview the subjects at their homes. Finger pricking was used toobtain blood samples, which were examined for malaria parasites. Data analysis was done using SPSS for Windows, version 11.0. Chi squared (χ²) or Gamma tests were used for analysis of categorical data, T-test was used for numerical data in two groups at a time andodds ratios were used to measure the strength of the association between independent and dependent variables. The level of significance was set to P<0.05 at 95% CI. In the qualitativepart, a purposeful sampling approach was used to select informants. Hand-written notes were taken during the interviews. The analysis started during the data gathering. Later, the material was read through in order to identify common themes, code parts of the text, identify similarities and generate concepts. It was found in this study that households with treated bed nets had significantly youngerhousehold heads (mean age 32.71 years) than those with untreated (36.72 years) and no nets (42.10 years). Heads of households with treated bed nets had a significantly higher overall level of knowledge about malaria, bed nets and insecticides - with an average score of 26.97 out of 29 knowledge questions (93%) - than households with untreated bed nets (83%) and without bed nets (73%). They were also significantly more literate (98% vs. 75% and 55%, respectively), and had spent more time in school (7.0 years vs. 4.5 and 3.3 years,respectively). Households with treated bed nets had a much higher average income per person per year (Tshs. 69,499) than households with untreated (Tshs. 29,773) and no nets (Tshs. 23,372), and the differences were significant. A higher proportion of the households without bed nets had heads who felt that insecticides were expensive (67%) than households with untreated (49%) and treated bed nets (18%). These findings were statistically significant. Almost all of the households with treated bed nets (99%) had heads who believedthat insecticides have no side effects, as compared to 85% of household heads with untreated, and 76% of households without, bed nets. Again, the differences were statistically significant. Almost all households with treated bed nets had heads who indicated thatinsecticides were available in their villages (99%), as compared to 78% of households with untreated nets and 63% of households without bed nets. These differences were statistically significant. There were also significant differences regarding the perception of insecticides. All household heads with treated bed nets felt that insecticides help “very much” in the prevention of malaria, as compared to 95% of households with untreated bed nets and 83% ofhouseholds without bed nets. Thirteen percent of households without bed nets and 4% with untreated bed nets said insecticides help to prevent malaria to “a certain extent”. The qualitative part of this study explored lay people’s own understandings of these issues. Itseemed clear that many people perceived malaria as a major health threat in their villages, and they thought that the seriousness and complications of the disease were the cause of their low economical status. The majority believed that malaria was caused by mosquito bites and that a lack of use of treated bed nets and a lack of destruction of mosquito breeding sites contributed to it. Many people knew how malaria could be transmitted and prevented, but some people did not seek medical treatment early due to social and local traditions and beliefs. Many people perceived the use of insecticide treated bed nets as an effective way of preventing malaria, but some believed that insecticides could cause harmful effects to humanbeings. Many informants said that people do not treat their bed nets because they don’t have enough money, and half said that they fear side effects of insecticides. Some said people do not treat their bed nets because they don’t understand very well how insecticides could prevent malaria and because they don’t see mosquitoes in their hamlets, especially during the dry season. Only one informant said the reason was that sometimes insecticides are not available in his village. This study concludes that low levels of knowledge about malaria, bed nets and insecticides, unaffordability of insecticides, unavailability of insecticides, misconceptions about theeffectiveness of insecticides, and myths about side effects of insecticides are associated with low rates of use and re-treatment of bed nets with insecticides. Younger persons seem to adapt to nets and insecticides significantly better than older persons. It is recommended that the designing and implementation of ITN programs, should consider all the factors associated with the use and re-treatment of bed nets. A joint effort from a combination of different disciplines and sectors is needed to overcome these obstacles.Behaviour Change Communication (BCC) activities should be designed in such a way that they would reach the entire population in the area, but special efforts should also be considered in order to reach the less beneficial groups who are the majority without ITNs.Innovative ways of reaching poor households should be explored. Income-generating projects should be considered in these villages since the purchasing power is so low. The price of bed nets and insecticides should be made affordable through subsidisation especially in areas where malaria has recently been introduced. Different types of colours, sizes and types of bed nets should be made available to satisfy the preferences of the customers. Several different sales points of bed nets and insecticides should be considered to maintain the availability. Any big construction project in developing countries should include a health impact assessment and mitigation program like the one that was implemented at the Lower Kihansi 5461 Hydropower project in Tanzania.