In eight impotent haemodialysed men with low plasma-zinc levels sexual function, including potency, frequency of intercourse, libido, and plasma testosterone, follicle-stimulating hormone, and luteinising hormone levels, was determined before and after therapy with zinc (four patients) or placebo (four patients). Dialytic administration of zinc strikingly improved potency in all patients and raised the plasma-testosterone to normal in the two with low pretreatment plasma-testosterone levels. Placebo did not improve sexual function in any patient. Zinc deficiency is a reversible cause of gonadal dysfunction in uraemia.