Repeated intraperitoneal injections of caffeine given to rats in dosages ranging from 4 to 16 mg daily throughout pregnancy resulted in significant resorptions and decrease in the birth weight ofthe offspring. These effects were dose-related. Developmental malformations, however, were not observed in the offspring at these dosage levels. These results indicate that caffeine, even in low doses which at the lower levels of the experiment may approximate to the daily human intake of a heavy coffee consumer, suppresses growth of embryonic and fetal tissues.