Although the relationship between androgens and the immune system has been well established, the immunomodulatory function of different kinds of androgens on the cellular immunity remains to be defined. In the present study, the in vitro influences of testosterone, dehydroisoandrosterone and androstenedione on the Con A induced proliferation of thymocyte were determined. The results showed that both dehydroisoandrosterone and testosterone suppressed the Con A induced proliferation of thymocyte, while dehydroisoandrosterone was less potent than testosterone. In contrast, relatively high doses of androstenedione augmented the proliferative activities of thymocytes. Taken together, these data implied that small structural changes of androgens result in markedly different biological effects. These findings suggest that the balance between these steroids may be a significant determinant in maintaining immune homeostasis.