In order to provide a contraceptive method in man, an attempt at inhibition of spermatogenesis was made by means of thermogenesis induced by artificial cryptorchidism. This experimental protocol consists of pushing up the testicles into the inguinal canal and keeping them there, each day during waking hours, by means of an adapted athletic supporter. Fourteen men volunteered for this protocol during a 6- to 12-month period. They all had a normal semen analysis before starting the experiment. The total sperm count, the sperm count per milliliter, the motility, the motile sperm count per milliliter, and the total motile sperm count dropped significantly after the first or second month; they reached their lowest values after the sixth month and remained stable during the next 6 months. At that time the average values reached were a total sperm count of 12 to 34 X 10(6)/ejaculate, a sperm count of 3 to 10 X 10(6)/ml, a motility of 21% to 34%, a motile sperm count of 1 to 3 X 10(6)/ml, and a total motile sperm count of 4 to 12 X 10(6)/ejaculate.