Bloodstained cuttings were extracted in 6 M urea. The extracts were subjected to ultrathin-layer polyacrylamide gel isoelectric focusing in the pH 4.5-5.4 range. After isoelectric focusing, Gc was detected by immunofixation in cellulose acetate membranes. This method permitted the successful typing of Gc in at least 4-month-old bloodstains maintained at room temperature. Bloodstains from 266 liquid blood samples of known origin were subjected to both this method and immunofixation conventional agarose gel electrophoresis with no phenotypic discrepancies observed. The Gc population data for whites from Baltimore, Md., were homogeneous with white sample populations from other geographical locations within the United States; while Gc data from northern U.S.A. black sample populations appeared to be heterogeneous compared with a southern United States black sample population. (Publisher abstract)