We report an open, prospective, randomized and double-blind study which compared two groups of patients without preoperative bacteriuria, undergoing transurethral urologic surgery. A first group received cefazoline 3 g perioperatively and a second group a single preoperative dose of cefotiam 1 g. A hundred patients were included in each group which were well matched on all essential characteristics, risk factors, surgery, anesthesia and postoperative temperature. The incidence of postoperative infection (bacteriemia and bacteriuria) was the same in both groups (16%). It is concluded that in transurethral urologic surgery performed in patients without preoperative bacteriuria, 1 preoperative dose cefotiam is as efficacious as 3 perioperative doses cefazoline.