Systemic lupus erythematosus occurs with much greater frequency in females than in males, and in some reports, researchers suggested that treatment with androgenic hormones might have therapeutic effects in this disease. The authors report a case of systemic lupus erythematosus in a hypogonadal male with Klinefelter's syndrome who was treated with testosterone in doses sufficient to normalize the serum level of this hormone to the adult male range. Hematologic and serologic abnormalities, including elevated levels of anti-DNA antibodies and depressed complement levels, returned to normal within 9 months of increasing the testosterone dose. The findings in this patient indicate that androgenic steroids can exert significant effects on immune parameters, and suggest that effects of androgens on the immune system may contribute to the sexual dimorphism of autoimmune disease.