Colloidal gold was used to detect extremely small amount of proteins electrotransferred on nitrocellulose membrane after sodium dodecyl sulfate polyacrylamide gel electrophoresis. Clearly deep wine-red bands of proteins were obtained by using 0.002∼0.005% colloidal gold solution stabilized with Tween 20. The sensitivity was in the same range as silver staining of polyacrylamide gel and enough to detect nanogram order of proteins applied on the gel.