Abstract A quantitative histomorphometric assessment of testicular spermatogenesis was undertaken on testes from rats which had received 1-amino-3 chloro-2 propanol hydrochloride (CL 88, 236) at oral doses of 0, 50, 250 or 500 mg/ kg/day for 12 weeks. Rats which developed epididymal sperm granulomata or severe atrophy of the germinal epithelium were excluded from quantitative examination. Pathological changes in the epididymis and seminiferous epithelium were not strongly correlated. CL 88, 236 administered at 50 mg/ kg/day was without effect on the histomorphometry of the seminiferous epithelium, although epididymal lesions occurred at this dose. At higher doses a quantitative reduction in testicular spermatids was evident. It appears important to differentiate between the selective antifertility action of CL 88, 236 on the biochemistry of epididymal spermatozoa and the disruption of epididymal physiology, and testicular spermatogenesis found at unusually high doses.