OBJECTIVE To evaluate the impact of maintenance haemodialysis and live-related renal transplantation on the reproductive potential of men with end-stage renal disease. METHODS The plasma levels of testosterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were determined, and semen analysed, in 19 men (22-41 years old) with advanced uraemia after 6 months of dialysis and again 6 months after renal transplantation. Eight patients who had azoospermia or severe oligospermia underwent testicular biopsy after 6 months of dialysis and again 6 months after the transplant. RESULTS Following dialysis, levels of testosterone were low in 17 patients and levels of LH and FSH were elevated in 15 and eight patients, respectively. Four patients each had azoospermia and severe oligospermia. The testicular tissue was hypospematogenic in three patients, showed late-maturation arrest in four and germ cell aplasia in one. After renal transplantation, testosterone and LH levels returned to normal in 15 and 13 patients, respectively, while FSH levels became normal in only two patients. The recovery of testosterone and LH levels after transplantation was statistically significant. Semen quality improved in 13 patients, with the improvement in sperm density and motility being statistically significant. Testicular histology revealed normal spermatogenesis in four patients, while three continued to show late-maturation arrest. The wives of five of the transplanted patients conceived. CONCLUSIONS The impairment of testicular function seen in advanced uraemia is not reversible by maintenance haemodialysis. In contrast, after successful transplantation, steroidogenic function became almost normal while spermatogenic function showed a striking if incomplete recovery.