To determine whether Schistosoma haematobium infection is associated with functional renal disease, renal function tests and intravenous urography were carried out on 75 hospitalized Egyptian farmers with urinary schistosomiasis. All patients had urographic abnormalities, and nearly half had bilateral obstructive uropathy. Bacterial urinary-tract infection, commonly due to Salmonella, was found in one-third of the patients. Significant impairment of maximal urinary concentrating ability was present among 49 patients with bilateral obstructive uropathy, or bacterial infection, or with both. Fifteen-minute phenolsulfonphthalein excretion was frequently abnormal among these same patients, but in the presence of anatomic distortion of the lower urinary tract this finding could not be attributed with certainty to renal dysfunction. There was no correlation of symptoms, urine findings, radiographic changes, or impaired renal function with age of the patient; hyperendemic urinary schistosomiasis may affect children as seriously as adults. Urinary tract obstruction due to schistosomiasis in Egypt is associated with functional renal disease, and bacterial infection of the urinary tract may also contribute to decreased renal function.