Twenty-one women were studied nhu had received propylthiouracil or methimuzole during 26 pregnancies. Four of the infants had a goiter at birth, and 3 of these had neonatal thyrotosicosis. In 2 children neonatal thyrotocicosis eas not evident at birth because of maternal antithyroid therapy. Five children had congenital defects. Two mothers nere responsible for 4 of the children with abnormalities, and both mothers had been treated with thiourea drugs for long periods, ranging from 7 to 11 years. The majority of children who are exposed to these drugsin uteroappear to have no subsequent ill effects. However, prolonged therapy with these agents may be undesirable.