The fate of the dilated renal pelvis that is induced in fetal rats following prenatal exposure to nitrofen was evaluated. Groups of Long Evans rats were exposed to 0, 6.25, 12.5 or 25 mg/kg of nitrofen on gestation days 7-16. Renal morphology of the offspring were determined on gestation day 21 and postnatal week five. The postnatal cohort was tested at two weeks of age for their ability to excrete an osmotically concentrated urine. In addition to confirming the effect on the fetal papilla, a reduced renal concentrating ability in the neonate was demonstrated. As was the case with adriamycin, the poor performance in function test was associated with permanence of the morphological effect. By utilizing a standardized semi-quantitative procedure to describe the status of the kidneys and ureters during development in combination with physiological assessment of organ performance, it was possible to assess the morphological and functional development of the kidney. It is suggested offspring be monitored during postnatal development when alterations of the fetal renal papilla are observed in standard teratology bioassays in order to determine whether the effect is transient or permanent.