During the last 4 years we succeeded in proving in experiments in rats and bulls that a cup-shaped silicone-dacron prosthesis may be used as Sperm-reservoir. Spermatozoa--aspirated from this reservoir and stored as pellets in liquid nitrogen over 6 weeks--induced pregnancies and normal births in 50 percent of inseminated cows. Because of aplasia or long stenosis of the vas deferens 26 prostheses (20 X 8 X 8 mm) were implanted upon the epididymis in 14 patients. Percutaneous aspirations up to 7 months after operation showed up to 105 million spermatozoa persingle aspiration. The number and the motility of the aspirated spermatozoa varied considerably from one puncture to the next. Quality and quantity of spermatozoa decreases in correlation with longer postoperative delays. Average aspiration-time was 3 months and positive sperm counts were obtained on an average for 2 months. Insemination of the patients' wives with the aspirate did not result in any pregnancy so far. In "hopeless cases" presenting excretory azoospermia and aplasia or long stenosis of the vas, we try to obtain maximal numbers of spermatozoa by early and frequent aspiration of the implanted alloplastic reservoir for well "timed" direct insemination and deepfreezing.