The authors sought to establish whether bacteriuria or candiduria would develop in patients with a noninfected, obstructed renal collecting system after placement of a percutaneous nephrostomy tube. Tubes were placed in 27 sterile systems in 25 patients. Urine was cultured at 7-10-day intervals, and urinalysis was performed. Bacteriuria and pyuria were defined on the basis of laboratory values of greater than or equal to 10(4) colony-forming units per milliliter and greater than or equal to five white blood cells per high-powered field, respectively. Twenty-two systems were followed until all demonstrated multiple organisms. No clinical symptoms were related to bacteriuria.