The relationship between reduced glutathione (GSH) level and glutathione S-transferase (GST) activity in erythrocytes was examined, using sheep erythrocytes, which have varying GSH concentrations, and dog erythrocytes with an inherited high concentration of GSH. There was a positive correlation (r=0.529,p<0.001) between the GSH level and GST activity in sheep erythrocytes. In dog erythrocytes, the GST activity in high-GSH cells was significantly (p<0.001) higher than that in normal-GSH cells. These results indicate that the activity of GST in erythrocytes is directly correlated with the intracellular GSH level
