ABSTRACT T cells are considered to be unresponsive to testosterone due to the absence of androgen receptors (AR). Here, we demonstrate the testosterone responsiveness of murine splenic T cells in vitro as well as the presence of unconventional cell surface receptors for testosterone and classical intracellular AR. Binding sites for testosterone on the surface of both CD4+ and CD8+ subsets of T cells are directly revealed with the impeded ligand testosterone‐BSA‐FITC by confocal laser scanning microscopy (CLSM) and flow cytometry, respectively. Binding of the plasma membrane impermeable testosterone‐BSA conjugate induces a rapid rise (<5s) inCa2+i of Fura‐2‐loaded T cells. This rise reflects influx of extracellular Ca2+ through non‐voltage‐gated and Ni2+‐blockable Ca2+ channels of the plasma membrane. The testosterone‐BSA‐induced Ca2+ import is not affected by cyproterone, a blocker of the AR. In addition, AR are not detectable on the surface of intact T cells when using anti‐AR antibodies directed against the amino and carboxy terminus of the AR, although T cells contain AR, as revealed by reverse transcription‐polymerase chain reactions and Western blotting. AR can be visualized with the anti‐AR antibodies in the cytoplasm of permeabilized T cells by using CLSM, though AR are not detectable in cytosol fractions when using the charcoal binding assay with 3H‐R1881 as ligand. Cytoplasmic AR do not translocate to the nucleus of T cells in the presence of testosterone, in contrast to cytoplasmic AR in human cancer LNCaP cells. These findings suggest that the classical AR present in splenic T cells are not active in the genomic pathway. By contrast, the cell surface receptors for testosterone are in a functionally active state, enabling T cells a nongenomic response to testosterone.—Benten, W. P. M., Lieberherr, M., Giese, G., Wrehlke, C., Stamm, O., Sekeris, C. E., Mossmann, H., Wunderlich, F. Functional testosterone receptors in plasma membranes of T cells. FASEB J. 13, 123–133 (1999)