The toxicological in-patient hospital in Budapest is responsible for the care of chemically poisoned persons from a population of 3 million. A population-based prospective epidemiological study of all pregnant women admitted from 1985 to 1993 was used to evaluate effects of large doses of chemicals on human fetal development. Of 559 self-poisoned pregnant women identified, two died from the poisoning. A total of 213 fetuses were in the first month of their postconception development. Of these, 126 had evaluated pregnancy outcomes: 111 ended in very early loss, 3 ended in clinical miscarriage, and 12 survived to delivery. (In addition 73 pregnancies were terminated and one pregnant woman died.) The 12 liveborn infants had two congenital abnormalities that were probably not related to their mother's self-poisoning. Though based on small numbers, these findings are consistent with an "all-or-nothing" effect of chemical poisoning very early in human gestation.