A large sample of cross sectional profiles of seminiferous tubules from the left testes of five Albino Swiss rats 6 months after left unilateral vasectomy was compared with those of sham-operated controls. Using the classification of Leblond & Clermont (1952), based primarily on the morphology of the spermatids, the frequency of each stage of the seminiferous cycle was recorded. Profiles were also analysed for distension, reduction in epithelial area and changes in spermatocyte numbers. The lack of significant alterations in either the seminiferous cycle, the numbers of pachytene spermatocyte nuclei or epithelial area in the tubular profiles indicated that there was no alteration in spermatogenic rate after vasectomy. The lack of tubular distension, reduction in spermatocytes per unit length of perimeter or of the presence of mature spermatozoa at inappropriate stages of the cycle indicated the absence of sperm retention. The study makes clear that, at least in Albino Swiss rats 6 months after vasectomy, the apparently healthy tubules were indeed normal.