An improved method for subtyping Pi in old bloodstains.

Immunofixation procedures were used for detecting alpha-1 antitrypsin protease inhibitor (Pi) phenotypes in bloodstains. Neuraminidase elution of bloodstains, together with isoelectric focusing, immunofixation, and silver staining techniques, makes possible Pi subtyping in old bloodstains. No extra bands appear when the storage time is no longer than three months.