We have carried out a prospective, randomized controlled trial of perioperative prophylaxis with cefuroxime and piperacillin in 53 recipients of renal allografts. Twenty-seven patients received antibiotic prophylaxis with three doses of cefuroxime 750 mg and piperacillin 4 g, and 26 patients received no prophylaxis. Risk factors for infection were well matched. Infection rates were analysed for the periods 0-5 days and 0-14 days post-transplant. In the first 5 days, patients receiving antibiotics had fewer infections (3 vs. 11, P = 0.04) but by 14 days this difference was no longer apparent (21 vs. 30, P = NS). There was a total of 15 wound infections, which were more common in the control group both at 5 days (1 vs. 5, P = NS) and at 14 days (4 vs. 11, P = 0.027). Urinary infections were unaffected by prophylaxis. We conclude that perioperative antibiotic prophylaxis results in a modest but worthwhile reduction in the incidence of wound infections after renal transplantation.