A simple and sensitive method for the simultaneous visualization of glutathione peroxidase and catalase on polyacrylamide gels is described. The procedure included: (I) running samples on a 7. 5% polyacryla-mide gel, (2) soaking the gel in a certain concentration of reduced glutathione (0.25–2.0 mM). (3) soaking the gel in GSH plus H_zO_z or cumene hydroperoxide, (4) finally staining with a 1% ferric chloride I% potassium ferricyanide solution. The best concentration of glutathione for simultaneous visualization of glutathione peroxidase and catalase was 0.25rnM; I.5mM glutathione was the best concentration for visualization of glutathione peroxidase alone. The method is sensitive enough to detect catalase and glutathione peroxidase in mouse liver homogenates and also it is specific for glutathione peroxidase since other peroxidases such as lactoperoxidase, horseradish peroxidase and glutathione S-transferase cannot be visualized. Using this method, it was found that unlike catalase. glutathione peroxidase is heat resistant (68°C. 1min), but sensitive to 10mM sodium iodoacetate.