In 284 patients with a great variety of primary testicular disorders registration of spermatogenesis was performed with the testicular biopsy score count method described by the author. Correlation analyses between the score count steps and gonadotrophin excretion show a great rise when spermatozoa (late spermatids) disappear from the testis. There is a high correlation between the per cent of tubuli possessing spermatozoa and the gonadotrophin level. Disappearance also of spermatids or spermatocytes or spermatogonia induces no further rise in gonadotrophins and no separate effect of these cells on gonadotrophins could be demonstrated. Some influence upon the gonadotrophin level was found when only Sertoli cells were present but this was small as compared with the effect of spermatozoa. It is concluded that the stage of spermatogenesis involved in the testicularhypophyseal feed-back mechanism in man is the last stage where the spermatozoon is finished and matured. The way this stage exerts its influence upon the gonadotrophin level is briefly discussed.