SUMMARYRed cell GSH concentrations were measured in 83 pure-bred and 65 cross-bred Tasmanian Merino sheep. A bimodal distribution was found; 40% of sheep had mean GSH values of 27·3 ± 1·2 mg and 60% had 92·2 ± 1·5 mg/100 ml red cells. Family data are limited, but they suggest that this difference is under genetic control, the gene for low GSH levels being dominant to that for high. Unlike GSH-low type Finnish Landrace sheep, GSH-low type Merino sheep do not have lower than normal red cell sodium and potassium concentrations.