Testis weight as a percentage of body weight did not change following bilateral ligation of the efferent ducts (EDL) close to the epididymis, whereas following removal of part of the epididymis between the site of ligation and a point close to the junction between the caput and corpus (PCE), testis weight first rose linearly until Day 4 and then showed an exponential decrease between Days 4 and 28. After EDL, the perimeter of the seminiferous tubules rose for the first 7 days and then remained elevated, whereas after PCE, there was a linear decrease between Days 4 and 28. Following EDL, the percentage of altered and degenerated tubular cross-sections rose to about 30% and 10%, respectively, during the first 7 days after operation and then remained constant; after PCE, the percentage of altered tubules reached a maximum of 54% by 4 days and then fell, whereas the percentage of degenerated tubules continued to rise to 95% by 28 days. It would appear that all the effects of removal of a portion of the epididymis cannot be explained by blockage of the excurrent ducts, and a specific endocrine effect of the epididymis on the testis is proposed.