This study was designed to describe the reproductive biology of a sample of wild-caught brown treesnakes and to determine the effect of increased food intake (nutrition) on the development of the testis and sexual segment of the kidney, and on sperm storage in the vas deferens in captive males. The wild snakes were trapped and preserved within 24 h, in December 1999, from a snake trap-line in northern Guam. In the nutrition experiment adult snakes were matched for snout–vent length and separated into three groups. Groups 1 and 2 were fed a high-calorie diet for 8 and 4 weeks, respectively. Group 3 males, the control group, received a low-calorie diet and were preserved at 7 weeks. In the wild sample all snakes above 1035 mm snout–vent length were undergoing spermatogenesis, had a well developed sexual segment of the kidney, and had sperm stored in the vas deferens. In all experimental groups, spermatogenesis and development of the sexual segment of the kidney was terminated or inhibited, and in most snakes sperm were absent from the vas deferens. Blood levels of stress hormones (i.e. corticosterone) and reproductive hormones (androgens) were not measured. However, a previous study reported that the stress of captivity causes an increase in plasma levels of corticosterone in brown treesnakes, and other studies on squamates indicate that high corticosterone levels can disrupt reproductive hormones and shut down the reproductive cycle.