1. Erythrocytes (RBC) from control and marginally riboflavin-deficient subjects were fractionated into nine fractions using a discrete density gradient.
2. Glutathione reductase (NAD(P)H: glutathione oxidoreductase; EC 126.96.36.199) activity and aspartate aminotransferase (EC 188.8.131.52) activity (with and without the appropriate co-enzymes) reduced glutathione, methaemoglobin, sulphaemoglobin and oxyhaemoglobin and susceptibility to peroxide were measured in RBC in the different fractions.
3. Glutathione reductase and aspartate aminotransferase activities and concentrations of reduced glutathione and oxyhaemoglobin all declined with age, while melhaemoglobin, sulphaemoglobin and susceptibility to peroxide increased with age.
4. The only significant differences noted in the RBC from marginally-riboflavin-deficient subjects by comparison with controls, were lower glutathione reductase activities and higher concentrations of methaemoglobin.
5. The role of riboflavin in those sytems controlling RBC integrity is discussed.