Red cell glutathione reductase (E-GSR) activity in 3 patients with mos46,XY/47,XY,+8 was higher than the mean value in controls, confirming the previous assignment of the E-GSR locus to chromosome 8. In a infant with a terminal deletion of the short arm of chromosome 8, 46,XX,del(8)(:p21 leads to qter), E-GSR activity was markedly lower than in infant controls. The authors suggest that the E-GSR locus is in the region 8p21 leads to pter.