Erythrocytes of both G‐6‐PD deficient humans and Dorset sheep, an animal model with an erythrocyte G‐6‐PD deficiency, both responded in a dose‐dependent manner to the oxidant stress of MLHP as measured by decreases in G‐6‐PD activity, increases in METHB levels and decreases in GSH. However, the human G‐6‐PD deficient erythrocytes were considerably more sensitive to the formation of METHB than the sheep erythrocytes while the reverse was the case for the GSH parameter. The results suggest a qualitative difference in the response of sheep erythrocytes and human G‐6‐PD deficient erythrocytes to MLHP that seriously questions the value of the sheep erythrocyte as a quantitatively accurate predictive model.