Three forms of the androgen receptor have been characterized at high ionic strength in partially purified cytosol and nuclear fractions of rat ventral prostate, epididymis, testis, and seminal vesicle by ion exchange chromatography on phosphocellulose, gel filtration in Sephadex G-200, and sedimentation in sucrose gradients. The three forms have the following properties, respectively: elution from phosphocellulose at 0.15--0.20, 0.3--0.5, and 0.20--0.32 M KCl; gel filtration radii of 53, 36, and 22 A; sedimentation coefficients of 5.0S, 3.6S, and 3.0S; frictional ratios of 1.65, 1.4, and 1.0; and molecular weights of 115,000, 55,000, and 29,000. In testis and epididymis cytosol, the 53 A, 5S form was more abundant than the 36 A, 3.6S form. In ventral prostate, the 36 A, 3.6S receptor was the predominant form. Variable amounts of all three forms were observed in seminal vesicles. Conversion from 36 A, 3.6S to 22 A, 3.0S was induced by heating ventral prostate cytosol and could be blocked by serine protease inhibitors. The 22 A, 3.0S receptor fragment from heated prostate cytosol was similar in size and symmetry to receptor extracted in 0.5 M KCl from prostate nuclei labeled in vivo. Extracts of epididymis and seminal vesicle nuclei contained both 36 and 22 A forms.