 In mice fed the whey protein-rich diet between 17 months and 20 months of age, the heart tissue and liver tissue glutathione content were enhanced above the corresponding values of the casein diet-fed and Purina-fed mice.Mice fed the whey protein diet at the onset of senescence, exhibited increased longevity as compared to mice fed Purina mouse chow over the 6.3 month observation period extending from the age of 21 months (corresponding to a human age of 55 years) to 26–27 months of age (corresponding to a human age of 80 years), during which time 55% mortality was observed.The corresponding mean survival time of mice fed the defined casein diet is almost identical to that of Purina-fed controls.