This study was designed to test the hypothesis that high urinary output in patients with an indwelling bladder catheter tends to protect the patients from acute urinary tract infection. Thirty-five cases of acute spinal cord injury were analyzed for average daily urine volume and frequency of acute urinary infection (defined as oral temperature above 101 F and requiring treatment for the infection). The study period encompassed the time from entry into the Rehabilitation Unit until a definitive effort was made to remove the catheter, a mean of 59 days. Twenty-six patients developed acute urinary infections while nine did not. Mean 24-hour urine output in the two groups was 2530 cc and 2540 cc, respectively. The only difference which could be found was a significant decrease in urinary output in the symptomatic group during the seven days preceding onset of acute infection.