It has been suggested that the more than 1 million black Americans with the A-variant of glucose-6-phosphate dehydrogenase deficiency (G6PD) are at risk for adverse hematologic effects due to inhalation of ambient levels of oxidant gases. To evaluate this hypothesis studies were performed that included direct exposure of human G6PD-deficient red cells, and of mouse strains with different G6PD levels, to the oxidant gases ozone and nitrogen dioxide. Using the oxidant drug phenylhydrazine in part as a point of comparison, conservative extrapolation of the data indicates that exposure to levels of ozone or nitrogen dioxide at least one and probably two orders of magnitude above the LD50would be required for any hematologic effect to be observed of pertinence to G6PD deficiency. It is concluded that there is no reason to remove or preclude from the workplace black employees with the common A-variant of red cell G6PD deficiency who potentially are exposed to oxidant gases.