SUMMARYThe production of testosterone (Te) and androstenedione (A) has been studied in twenty‐three patients with chronic renal failure. Four of the patients were being prepared for haemodialysis (HD) treatment — non‐HD patients — nineteen were on chronic HD treatment, five of whom had been nephrectomized bilaterally. Data are presented on plasma Te and A levels, on the response to HCG and on changes after HD. The Metabolic Clearance Rate (MCR), blood production rate and the mutual interconversion of both steroids were determined together with the plasma sex hormone binding globulin capacity.In all groups of patients, plasma levels of Te were low and stimulation with HCG resulted in an insufficient increase in plasma Te levels, indicating Leydig cell deficiency in chronic uraemic males. In addition, a tendency to increased metabolic breakdown of Te was observed, most probably caused by a deficient synthesis of the sex hormone binding globulin. In patients with high peripheral degradation of Te, the testicles were able to produce about normal amounts of Te.In the non‐HD patients an increase in the MCR and blood production rate of A was found. This may be due to an alteration in the testicular steroid secretion. The other groups of patients did not show differences in the production of A when compared with normal males. No significant changes in plasma levels of Te and A were observed during HD treatment.The picture emerging from our data is similar to the one observed in population groups with severe protein mal