Twenty-three patients who underwent abdominoperineal resection for rectal adenocarcinoma were entered into a prospective study to determine the efficacy of periodic instillation of Betadine into the urinary drainage system as a prophylactic measure for catheter-associated urinary tract infections. We decided to use a control group of 33 consecutive patients done in the period just preceding the starting of this prospective study. In both groups the mean duration of the Foley catheter drainage was similar. Eight of eight female patients in the treatment group and six of seven patients in the control group developed a urinary tract infection. However, only five of 15 male patients (33%) in the treatment group whereas 16 of 26 males in the control group (61%) developed a urinary tract infection. Thus, the addition of Betadine in the drainage system of urinary indwelling catheters was associated with a 50% decrease in the incidence of urinary tract infections in males.