Bladder-aspirate urine samples (N = 428) were cultured for the presence of fastidious microorganisms. These samples were obtained from 190 patients with urinary tract disease or symptoms suggesting infection of the urinary tract in whom standard bacteriologic investigation had failed to indicate bacterial infection. Ureaplasma urealyticum was recovered alone or in association with other microorganisms from the bladder urine of 75% of patients with reflux scarring and abnormal renal function. Ureaplasma organisms were localized to the upper urinary tract in 80% of patients with bladder counts greater than 10(3) colony-forming units per ml. The results indicate that microorganisms not conventionally associated with urinary tract infection are recoverable from the bladder urine of a high percentage of patients with so-called "sterile pyelonephritis," in which group of patients these microorganisms may contribute to progressive renal disease.