The testes of adult male rabbits were studied with the light and electron microscopes at intervals of up to 9 months after vasectomy or a sham operation. No changes were detected in any rabbits killed at intervals between 2 weeks and 4 months after vasectomy or in 1 of 2 rabbits prepared 6 months after vasectomy. In one rabbit killed 6 months after operation spermatogenesis was severely depressed and a spermatic granuloma was present near the epididymis. All 3 rabbits killed 9 months after vasectomy exhibited a greater than normal number of multinucleate spermatids, and this condition was most pronounced in one rabbit in which the epididymis and vas deferens were the most greatly distended of all the vasectomized animals. No changes were observed in animals that received a sham operation.