Repeated blood collection from pregnant rats was examined for effects on fetuses. Blood was collected four times from the same pregnant rat (0.5 ml each time and 2 ml in total). In Experiment 1, blood was first collected on day 9 of gestation and then repeatedly at 1, 4 and 18 hr intervals. In Experiment 2, blood was collected once on day 6 of gestation and then repeatedly on days 9, 12 and 15. Decreases in body weight and food consumption of the pregnant animals were noted in both experiments and considered due to restraint and needle puncture. In neither experiment could any effects be found on day 20 of gestation with regard to viability, fetal weight, placental weight or gross malformation. The results indicated that this regimen of blood collection could be used in developmental toxicity assessment studies.