Eighty-nine pregnancies, at risk for placental insufficiency, were monitored with serial oxytocin challenge tests (OCT) and estriol determinations on 24-hour urine collections. Intraamniotic catheters were used to accurately record intrauterine pressure in 63% of the tests; 114 of the 116 tests (98%) were adequate for interpretation. Thirteen positive tests were recorded; however, in only 2 cases did the positive OCT predict a dysmature-postmature infant when estriol determinations were normal. Prompt delivery following a positive OCT can significantly reduce the incidence of fetal wastage.