The glutathione-peroxidase (GSH-Px) activity in erythrocytes was determined in 42 men with severe acne and 47 women with acne--26 of a moderate degree and 21 severe. The male acne patients had significantly lower GSH-Px levels than the controls. The women with acne did not differ significantly from the controls in this respect when patients and controls using oral contraceptives were excluded. Both the female controls and the women with acne using oral contraceptives had significantly higher GSH-Px values than the corresponding groups not using the pill. The pubertal acne girls had the same high GHSH-Px activity as women on oral contraceptives. In an open trial 29 patients were given 0.2 mg of selenium (as Na2Se O3) + 10 mg of tocopheryl succinate for their acne twice daily for 6-12 weeks. A good result was obtained, especially in patients with pustular acne and low GSH-Px activity, and the beneficial effect was usually paralleled by a slow rise of the GSH-Px activity. Some 6-8 weeks after withdrawal of the treatment the GSH-Px values had returned to the pretreatment levels.