This study was designed to determine the effect of methenamine on the frequency of urinary tract infections (UTI) in hospitalized patients after spinal cord injury. The study included 56 patients with neurogenic bladder dysfunction treated with intermittent catheterization. A group of 34 patients was treated with methenamine, 1g twice daily; the other group of 22 patients was the control group receiving no antimicrobial therapy. On a weekly basis urine samples from all patients were obtained for urinalysis and culture. A total of 500 urine samples were analyzed. The patients treated with methenamine had 23.4% positive urine cultures which was significantly lower than 57.5% in the untreated control group (p less than 0.001). Our data suggest that methenamine therapy is an effective prevention of UTI in paralyzed patients with neurogenic bladder dysfunction during the rehabilitation in hospital.