SUMMARY: In continuation of a previously reported study which showed that isolated non-flagellate germ cells of the rat testis metabolize progesterone to androgens, a search was made for the presence in these cells of specific progesterone and androgen receptors. Intact germ cells and their cytosol and nuclear fractions were incubated with 3H-labelled steroids; established analytical techniques were used to distinguish specific from non-specific binding. The steroid-protein complexes of progesterone, testosterone and dihydrotestosterone were partially purified by Sephadex column chromatography, acrylamide gel electrophoresis and sucrose density gradient analysis. The association constants of the three protein–steroid complexes were about 2 × 109 l/mol. The non-flagellate germ cells of the testis were found to have a higher binding capacity for progesterone than for testosterone and dihydrotestosterone. Epididymal spermatozoa did not bind progesterone specifically, but bound dihydrotestosterone to about the same extent as nuclei of non-flagellate cells. In extracts of seminal vesicles and prostate glands androgen binding was dominant, with negligible binding of progesterone. Synthetic progestogens (anti-androgens) competed effectively for the progesterone binding sites of the non-flagellate cells. In view of the finding that non-flagellate germ cells bind progesterone specifically and convert it to androgens, it is suggested that the metabolism of progesterone within the seminiferous epithelium of the testis may serve the purpose of maintaining an intratubular level of androgen for the support of spermatogenesis, independent of the extratubular secretion of androgen by the Leydig cells.