We evaluated 101 patients undergoing transurethral resection of the prostate in this open randomized study in which 51 received antibiotic prophylaxis and 50 did not (control group). In those patients receiving antibiotics, ceftriaxone 1 g was administered intravenously within 1 h before transurethral prostatectomy and a second dose was given 3-4 days postoperatively, within 1 h before the suprapubic catheter was removed. The groups had similar clinical and demographic characteristics. During the 28-day study period, bacteriuria appeared in six ceftriaxone-treated patients and in 20 control patients (p < 0.005). On days 3-4 after the resection, only two patients who had received ceftriaxone had bacteriuria compared with 14 in the control group (p < 0.005). In addition, the incidence and duration of fever and length of hospitalization were shorter in the patients treated with ceftriaxone. In conclusion, these results support the use of prophylactic antibiotics in transurethral prostatectomy, even in patients at low risk of developing bacteriuria.