It is demonstrated in 30 rats that implantation of a cup-shaped silicone prothesis upon the head and the tail of the epididymis can serve as an alloplastic spermatocele. The implantation of six similar protheses upon the epididymis in bulls confirms the results obtained in rats. Spermatozoa aspirated from this prothesis up to 4 months after operation showed good morphology and motility which improved: the earlier they were obtained after surgery, and the nearer the tail of the epididymis, the prothesis was implanted.