Heterozygosity is often shown to have a positive relationship with fitness-related characters. Sperm cells are fitness-related characters that show great variation among species, population's males and even within individual males. I will investigate relationships between heterozygosity and sperm characters in two bluethroat (Luscinia svecica) subspecies, L. s. svecica and L. s. namnetum. I have three main aims: 1) test whether previously found differences between the two subspecies in genetics and sperm characters will be upheld and/or strengthened. Further, I will add two aspects of sperm behavior that has not been studied in these subspecies before, namely velocity and proportion of motile sperm cells, 2) test the hypothesis that individual heterozygosity positively influences the expression of fitness-related sperm characteristics, and 3) investigate relationships among sperm characters at the level of the individual males, testing whether sperm morphology is related to sperm behavior. I used microsatellite genotyping (25 loci) to calculate the genetic diversity, and measured the sperm morphology (sperm length) and behavior (i.e. proportion of motile sperm cells and sperm velocity). There was little evidence for relationships between heterozygosity and any of the sperm characters, except for a significant relationship between heterozygosity and velocity when including data from all males (i.e. also males with < 10 motile sperm filmed). In support of previous studies, I found a strong genetic differentiation between the two subspecies, as well as differences in individual heterozygosity, in body size and red boarder width. Furthermore, the two subspecies differed strongly in sperm morphology, proportion of motile sperm and the within-male coefficient of variation in sperm length. There were no significant relationships between sperm morphology and aspects of sperm behavior. This study suggests a need for further prospects with larger sample sizes before a firm conclusion can be reached regarding the relationship between heterozygosity and sperm characters in the bluethroat.