Coliforms given intravenously usually fail to produce pyelonephritis unless urinary obstruction or other anatomic abnormalities are present. Previously, we had observed progressive pyelonephritis after hematogenous infection only in monkeys which seemed to have an abnormality of ureteral function. To further test this observation, unilateral ureteral instillation of Escherichia coli 04.06, and 0111 was carried out under base line pressure conditions. Animals infected with E. coli 04 showed unilateral absence of ureteral peristalsis, delay in excretion of radionuclide on scintiphoto studies, and ureteritis histologically. This study confirms that certain strains of E. coli cause ureteral dysfunction. So called nonobstruction pyelonephritis may really be obstructive.