Green iguanas (Iguana iguana) have been documented to become aggressive during their breeding season and during the menstrual cycles of their human female caregivers. Because of their large size, these reptiles have the potential to inflict severe bite wounds. Identifying a method to control aggression in these animals is needed to minimize the likelihood of injury to their handlers. The purpose of this study was to evaluate the effect of mammalian leuprolide acetate on the testosterone levels of captive, intact male green iguanas. Eighteen adult male green iguanas were used for the study. Testosterone levels were determined via radioimmunoassay. Group 1, the control group, did not receive any mammalian leuprolide acetate, group 2 was administered a single dose of 0.2 mg/kg mammalian leuprolide acetate IM in the right forelimb, and group 3 received a single dose of 0.4 mg/kg mammalian leuprolide acetate IM in the right forelimb. Blood was collected for testosterone assays on day 0, before treatment, and days 1, 4, 7, 14, 21, 28, and 35 post-treatment. There was a significant difference in the testosterone levels within subjects (all animals across groups) over time (P = 0.007); however, there was no significant difference in testosterone levels between the different treatment groups (P = 0.6). There were significant differences within subject testosterone levels (all animals across groups) between days 0 and 1 (P = 0.001), days 0 and 4 (P = 0.035), days 0 and 28 (P = 0.02), and days 0 and 35 (P = 0.04). In all four cases, testosterone levels were lower on day 0 compared to the other days. The results of this study suggest that mammalian leuprolide acetate, at these doses, does not significantly reduce testosterone levels in captive male green iguanas.