Riboflavin status was determined in 16 Oriental males and females who were residing off the Oregon State University campus. Before and after these subjects had received 10 mg of riboflavin daily for 7 days, we measured erythrocyte glutathione reductase (EGR) activity with and without FAD added in vitro and erythrocyte total riboflavin levels (RBC B-2). Riboflavin status was assessed by the EGR activity coefficient (EGRAC) (EGR activity with FAD added in vitro / EGR activity without FAD added in vitro). The subjects' dietary intake of riboflavin, protein and calories was estimated from their self chosen diets which were recorded for 3 days before the riboflavin supplementation. Both sex groups had adequate mean levels of riboflavin, protein and calories in their diets. Further, none of the subjects had an intake less than two-thirds of the recommended dietary allowances (FNB, 1980) for riboflavin. Before riboflavin supplementation 5 of the 9 males and 2 of the 7 females had EGRAC greater than or equal to 1.2, suggesting that they were at high risk of marginal riboflavin deficiency, and to have a normal EGRAC they may need an intake of riboflavin greater than the present recommended allowance. In all of the subjects, EGRAC decreased in response to the riboflavin supplements. Additionally, the subjects' RBC B-2, EGR basal activity (without FAD added in vitro) and FAD stimulated EGR activity increased significantly (P < 0.01) after 7 days of riboflavin supplementation. Although the RBC B-2 concentrations were lower than those reported by Bessey, Horwitt and Love (1956) and Bamji (1969), this measurement correlated significantly with EGRAC (r = -0.64, P < 0.01), EGR basal activity (r = 0.74, P < 0.01) and FAD stimulated EGR activity (r = 0.57, P < 0.01). Dietary riboflavin intake whether expressed as total riboflavin intake per day or riboflavin intake per 1000 Kcal was not correlated to any of these biochemical tests made before riboflavin supplementation. RBC B-2 values obtained from these 16 Orientals were similar to those obtained in 5 Caucasian subjects, indicating that these low values were not due to genetic differences. / Graduation date: 1986