When caffeine (1,3,7-trimethylxanthine) was introduced into the diet of rats throughout pregnancy and lactation at levels of consumption of 10 mg/kg/day, offspring of successive pregnancies showed growth reductions. This finding was not accompanied by teratogenic effects. However, following four pregnancies severely reduced offspring growth and neonatal mortality was demonstrated. The birthweights of these offspring were 72.5% of control. This study mimicked the mode of intake and quantities of caffeine consumed in many societies.