The urinary catheter must be respected. Its use is essential in many situations. In patients with debilitating general disease or obstructive urologic lesions it is not surprising when bacteriuria, pyelonephritis, or even bacteremia follow catheterization. The indwelling catheter must be expected to elicit a foreignbody reaction, and the cellular elements and bacteria sometimes persist in the urine as long as three months after removal of the catheter. Longer persistence should raise the question as to whether the urinary system is emptying efficiently. The hazards of using the catheter in a given case must be weighed against the probable consequences if it is not used. To be both safe and reliable, the technique of catheterization must be carried out aseptically. It demands adequate facilities, personnel, and preparation. It should be done with adequate exposure and good lighting, by two nurses or a physician and a nurse.