Polyacrylamide gel isoelectric focusing was carried out under the following conditions. The gel was 200 by 115 by 0.5 mm in size and contained 6.2 percent in total concentration of monomer and 3.2 percent in the total monomer due to a cross-linking agent. Blood was obtained from 100 normal donors with known Pi types. Stains were made by soaking pieces of clean cotton cloth in whole fresh blood and storing them at room temperature until used. A neuraminidase solution was used for extraction. Pi phenotypes from the 100 bloodstains were determined by isoelectric focusing techniques every week for a 4.5-month period. Neuraminidase elution of bloodstains, together with isoelectric focusing, immunofixation, and silver staining techniques, made Pi subtyping in old bloodstains possible. No extra bands appeared when the storage time was no longer than 3 months. 8 references and 5 figures (Author abstract modified)