A method for the detection of group specific component (Gc) by immunoblotting, following isoelectric focusing (IEF), is described. This isoelectric focusing method resolves the six common phenotypes of Gc using a narrow range pH 4.5 to 5.4 ampholyte. The Gc proteins were passively transferred from the IEF gel to nitrocellulose and detected with goat anti-Gc followed by peroxidase labeled anti-goat immunoglobulin (Ig) antibody. The increased sensitivity of this technique results in the typing of stains older than one year and also those stains with minimal concentrations of the Gc protein. The polyacrylamide gel can also be used for the subtyping of esterase D.