Partial absorption of oligospecific reagents by the particulate membrane fraction prepared from isolated interstitial cells grown in culture (the harvested cell population contained about 80% Leydig cells)suggests that membranes of Leydig cells carry antigenic specificities H-2K (11,25) and H-2D (4) but not antigens controlled by the I region. The results of absorption experiments have been confirmed by the methods at the level of individual cells; the native Leydig cells gave a positive reaction in the dye exclusion cytotoxic and immunofluorescent tests with he polyvalent regent B10D2 and B10 (directed against antigens of the regions H-2K through H-2I-E).