The effect on aging and survival of mild (2/3 of ad lib) chronic prenatal and postnatal undernutrition over 10 generations, or prenatal undernutrition only has been studied in rats. Both regimes of undernutrition used decreased body weights of animals as compared to the controls. Both undernourished groups had lower cholesterol levels and tumor incidence than the controls. The effects on survival depended not only on the time period of undernutrition but also on the age of the animals examined: chronic undernutrition resulted in lower survival of young adult animals (4-8 months) but higher survival than the controls in old age. Prenatal undernutrition only had no effect on young adult animals, gave higher survival than the controls at ages 8-18 months but considerably lower survival than controls in the old age: the underdevelopment of vital organs whose cells proliferate only before birth might have been the cause of such decreased longevity.