This project aims at the investigation of the effect of diet upon lens development and health. Nutrients under current study are tryptophan and other essential amino acids, vitamin E and selenium. A tryptophan deficit is cataractogenic during either prenatal or postnatal life. When the maternal (rat) diet contains only 65 mg% Trp (min. req. is about 150 mg%); rat pups have a normal wt. at birth and are only 50% normal wt. at weaning. Either an increase of total remaining dietary amino acids from 12.5 to 25% or omission of vitamin E from the maternal diet results in 30-90% incidence of pinhead nuclear opacities in the young upon examination at weaning. This morphological damage appears to be the result of an interference during development since we have been unable to find persistent biochemical perturbations in lens Na, K, H2O, protein content or proportion of lens crystallins. A similar maternal restriction of Phe/Tyr rather than Trp is not cataractogenic although the lenses at 21 days postpartum turn cloudy within minutes after death. Consumption of a 50 mg% L-Trp diet by previously well-nourished weanling rats also results in cataract but of a different sort. Opacities develop at the suture lines and eventually involve the majority of the lens. Neither omission of dietary vitamin E nor increase in dietary total amino acids affect the rate of appearance or severity of this cataract. Water content increases just prior to the transparency change and one entire crystallin group, the bH fraction, is absent from its normal position on a gel filtration column. The interaction of dietary selenium on lens development is now being studied.