Riboflavin status was measured by activation coefficient of erythrocyte glutathione reductase (EGRAC) in elderly and adolescent rural Gambians whose intakes were low. Fifty-one adolescents and 52 elderly subjects were each subdivided into six supplementation groups to receive 0.25, 0.5, 0.75, 1.0, 1.5, or 2.5 mg riboflavin/d on 5 consecutive days weekly for 5 wk. Before supplementation, EGRAC values were grossly abnormal and differed (p less than 0.005) between the two female groups [elderly subjects, 1.94 +/- 0.33 (means +/- SD); adolescents. 1.72 +/- 0.27] but not between the two male groups. With supplementation greater than 0.25 mg/d the values became nearly equal in the two age groups. Only at total intakes between 1.8 and 2.5 mg riboflavin/d did the subjects attain acceptable status, with a mean EGRAC of 1.3-1.4. Clearly there is a need for further study of the discrepancy between observed index values during supplementation and the accepted ranges of normality at intakes close to the recommended amounts.