Red cells from individuals deficient in glucose-6-phosphate dehydrogenase undergo increased autohemolysis when incubated in the presence of influenza-A virus. Normal red cells, but not those from individuals deficient in glucose-6-phosphate dehydrogenase, show increased activity of the hexose monophosphate shunt in the presence of the virus. This increase in shunt activity appears to be related to oxidation of cellular sulfhydryl groups.