After single stage Fowler-Stephens orchiopexy testicular atrophy is common. Previous experimental study in the scrotal testis of the adult rat has shown that ligation of the internal spermatic artery often causes focal testicular infarction or atrophy and exogenous human chorionic gonadotropin increases testicular blood flow. We questioned whether division of the internal spermatic artery in the undescended rat testis would also cause testicular injury and hypothesized that these changes might be prevented by administering human chorionic gonadotropin before vessel ligation. Two groups of 20-day-old Sprague-Dawley male rats were subjected to unilateral internal spermatic artery ligation. Group 1 (control) received no human chorionic gonadotropin, while group 2 received 10 IU human chorionic gonadotropin daily from days 3 to 17 of life. At 3 months testicular blood flow was quantitated using 141cerium radioactive microspheres. The results indicated that blood flow on the operated side was lower than on the nonoperated side but the change was not statistically significant. Human chorionic gonadotropin had no effect on blood flow to the operated testes. Gross testicular weights of operated versus nonoperated gonads were similar in rats that did and did not receive human chorionic gonadotropin. Pathological evaluation revealed normal histology in all testes. These results do not support the use of human chorionic gonadotropin preoperatively to stimulate collateral testicular blood flow.