SummaryTo investigate the role of the seminal vesicles (SV) and coagulating glands (CG) in fertilization in the rat, partial resections of the SV (25|X%–group B), 50|X%–group E, and 75|X%–group D) or bilateral resection of the SV alone (100%|X%group E), or together with the CG (group F) were undertaken. In other groups, bilateral resection of the CG only (group G), or bilateral resection of the CG with ipsilateral SV resection (group H) were performed. A group of sham‐operated rats served as controls (group A). There were no significant differences among groups A, B, C and D in the number of fertile rats post‐operatively but significant differences were evident in groups E, F, G, H when compared with the control group (P<0.01 for all groups). Only the fertile rats ere able to form copulatory plugs (CP) post‐operatively.Bilateral ligation of the SV ducts was performed in ten fertile rats. Post‐operatively, the proportion of fertile rats was decreased significantly (P<0.01). Removal of the ligatures resulted in a significant increase (P<0.01) in fertility. It was also demonstrated that the addition of rat seminal vesicular secretions (SVS) to epididymal sperm suspensions resulted in a significant decrease (P<0.001) in sperm motility.These results suggest that the SV and CG are necessary for fertility in rats, and that one role of SVS is the formation of a CP and not the maintenance of s