Seventy five patients requiring urethral catheterization for over 24 hours were treated with a latex Foley catheter with sustained release of chlorhexidine in a closed drainage system. While the catheter was indwelling, urinary concentrations of chlorhexidine were maintained at the level of 1 to 2 micrograms/ml in average in almost all patients. The catheter was highly effective in preventing the acquisition of catheter-associated bacteriuria in patients with initially sterile urine without systemic antimicrobial therapy. The acquisition rate of bacteriuria was 8, 16, 23, 35 and 74% on day 3, 4, 5, 6 and 7 with the catheter indwelling, respectively. The catheter was not effective in eradicating preexisting bacteriuria. Complications of the catheter were minimal.