Schistosomes can decrease the reproductive potential or castrate both invertebrate (snail) hosts as well as vertebrate (mouse, rat, and hamster) hosts. To determine if host castration occurs in human males, we examined testosterone levels in the sera of 38 Brazilian males, 16–35 years of age, who had Schistosoma mansoni infections. We found that individuals with intestinal schistosomiasis exhibited serum testosterone levels similar to those of noninfected controls. Four subjects with severe hepatosplenic disease also exhibited testosterone levels within the normal range. We did observe a negative correlation between parasite load (as predicted by fecal egg count) and testosterone levels but could not dissociate this relationship from the effect of age on either parameter. Therefore, in contrast to rodent models, host castration does not appear to be a usual side effect of human schistosomiasis.