This French multicentre, placebo-controlled, double-blind study investigated the efficacy of a single dose of cefotaxime 1 g iv in the prophylaxis of patients undergoing endoscopic extraction of urinary tract stones. Postoperative fever occurred in 12 patients in the placebo group and in nine in the cefotaxime group (no significant difference). The incidence of postoperative bacteriuria, between the first and third postoperative day, was significantly higher in the placebo group (15/60, 25%) than in the cefotaxime group (5/60, 8.5%). This controlled study clearly demonstrates the efficacy of antibiotic prophylaxis in endourological procedures. Cefotaxime significantly reduced the incidence of early postoperative bacteriuria without causing any significant side effects.