1. The production of Heinz bodies, after incubation of erythrocytes in the presence of hydrogen peroxide vapour, was significantly greater in erythrocytes with abnormally low glutathione peroxidase (GSH-Px) activity than in cells with normal enzyme activity.
2. The addition of the catalase inhibitor, sodium azide, to the incubation mixture, increased the formation of Heinz bodies after exposure to hydrogen peroxide vapour; the percentage of Heinz bodies was significantly greater in erythrocytes with low GSH-Px activity than in normal erythrocytes.
3. Erythrocyte GSH-Px deficiency thus predisposes the cell to Heinz body formation when exposed to oxidant stress.