The incidence of post-prostatectomy bacteriuria was measured in patients having no continuous bladder irrigation postoperatively, in those irrigated for 24 hours with chlorhexidine 1/5,000, and in those irrigated with normal saline. The infection rate after saline irrigation was greater than after chlorhexidine, but the infection rates after chlorhexidine irrigation and drainage alone were similar. The infection rate was higher in older patients, in those treated with retropubic rather than transurethral prostatectomies, in those who had postoperative catheters for more than 4 days, and in those admitted in acute retention of urine. The increase in infection rate associated with acute retention was seen only in the group treated with drainage alone postoperatively. Chlorhexidine irrigation appears to reduce the infection rate in these cases.