Sixty-four patients with obstruction or lesions of the ureter were, on 115 therapeutic sessions, submitted to internal diversion of urine employing JJ-catheters. Prior to the first treatment, 53% of the patients had been treated with nephrostomy catheters on account of postrenal obstruction. In 12% of the therapeutic sessions, the patients developed pyrexia of over 38.5 degrees C (101.3 degrees F) in the 24 hours immediately after introduction of the catheter. Only few patients had complications in the form of macroscopic haematuria, migration of the catheter, incrustations and perforation of the ureter. It is concluded that JJ-catheters provide a good and gentle method of relieving obstruction in the upper urinary passages. Bacteriological investigation and treatment of urinary infection is recommended prior to introduction of the catheter.