The purpose of this study is to determine the prevalence of riboflavin deficiency in an aged population. Riboflavin deficiency will be determined from the estimation of erythrocyte glutathione reductase activity of venous blood. The subjects will be selected from elderly patients who are in a hospital for chronic diseases, from those who visit the clinics of large municipal and private hospitals and from those residing in a home for the aged. The subjects will be classified according to age, dietary history, disease state, sex and ethnic group. Among those found deficient, the effect of vitamin repletion will be studied. Riboflavin will be given and the effect on erythrocyte glutathione reductase activity will be determined in order to see whether the deficienty in caused by a lack of absorption or utilization of the vitamin.