Abstnrct. The renographic pattern of excretion in 93 pregnant women with clinically suspected obstruction of the urinary tract was not found to differ significantly from what could be expected on the basis of previous reports concerning "normal" pregnancy. It is concluded that in pregnancy the renographic diagnosis of possible "pathological" urinary tract obstruction is seriously impeded by the very high incidence of impaired excretion of ''physiological'' character, especially on the right side. In cases of pain suggesting urinary tract obstruction, f i e finding of even severely impaired excretion does not conclusively establish an etiological relationship. The main importance of renography is to exclude or confirm abnormalities of renal uptake function which may require further investigation or treatment during, or after, pregnancy. Immediately following delivery, persisting renographic impairment of excretion suggests an obstruction of "pathological" significance.