To explore the ability of androgens to affect gene expression in Sertoli and peritubular cells in vitro, constitutively expressed pSV2-Luc and a regulated reporter containing an androgen response element (MMTV-Luc) were transiently transfected into these cells. Reporter expression was markedly affected by cell density and maturational age. Mibolerone-stimulated MMTV-Luc expression increased in Sertoli cells with animal age between 15 and 25 days, consistent with the developmental increase in androgen receptor concentration, but was not markedly age-dependent in peritubular cells. The antiandrogen hydroxyflutamide inhibited stimulation of MMTV-Luc expression by 1 and 10 nM testosterone in both Sertoli and peritubular cells, consistent with an androgen receptor-mediated event. In contrast, dexamethasone at 1 and 10 nM elicited no effect in Sertoli cells, but stimulated MMTV-Luc expression in peritubular cells. In this study, the androgen receptor/glucocorticoid receptor ratio was 2.4 and 0.06 in Sertoli and peritubular cells, respectively. Cotransfection of Sertoli and peritubular cells with a plasmid expressing the rat androgen receptor further increased the androgen-stimulated expression of MMTV-Luc. These data demonstrate the functionality of the androgen receptors in both Sertoli and peritubular cells in culture. Receptor expression appears to be a limiting factor in the response. The data are consistent with potential roles for both Sertoli and peritubular cells in androgen-mediated transcriptional events in the testis.