There is substantial evidence for alteration of oestrogen metabolism in both males and females with systemic lupus erythematosus (SLE). Low testosterone levels have been described in men with SLE, and it has been suggested that this may be a further predisposing factor to the development of the disease. Serum testosterone, oestradiol, FSH and LH levels were measured on two or more occasions in nine male patients with SLE. Similar estimations were performed on four other groups for comparison: ten male patients with rheumatoid arthritis, six male patients on long-term steroid therapy, eleven male patients with renal failure on long-term haemodialysis and eleven healthy male volunteers. Mean testosterone levels were significantly reduced in all disease groups and there was no significant difference between patients with SLE and those with other chronic disorders. Oestradiol levels were normal in all groups, but there was a trend to elevated mean levels of FSH and LH (p 0.05 for the haemodialysis group). Our results confirm that testosterone levels are low in males with SLE, but suggest that this is an effect of chronic disease, and therefore unlikely to be a pre-existing risk factor for the development of SLE in men.