Obesity has reached epidemic proportions in western industrialized countries and can be linked to a number of health risks such as hypertension, type 2 diabetes, coronary heart disease, and certain types of cancer. Obesity is due to a positive energy balance in the body that results in expansion of the adipose tissue caused by both hyperplasia and hypertrophy of adipocytes. Previous studies have found that MAPK activity is required in early stages of adipogenesis. It has also been reported that two of the MKPs, phosphatases known to dephosphorylate MAPKs, have a role in adipocyte differentiation. Based on this knowledge we carried out a systematic analysis of the expression and possible regulation of members of the MKP family during differentiation of 3T3-L1 preadipocytes. Results showed that most members of the MKP family are down-regulated during adipogenesis. We hypothesized that ectopic expression of one of the MKPs that was significantly down-regulated at early stages of differentiation, MKP-5, would have an effect on adipogenesis. Retroviral expression of MKP-5 in 3T3-L1 cells had a positive effect on adipocyte differentiation. In rodent obesity models ob/ob and Ay, most of the MKPs showed up-regulation in white adipose tissue, including MKP-5, with especially dramatic differences in subcutaneous fat depots. Although further studies are needed to verify these data, the results suggest that MKP-5, and possibly other MKPs, may have distinct roles during adipogenesis.