GC phenotypes were separated in a thin layer polyacrylamide gel by isoelectric focusing, transferred to nitrocellulose by a rapid capillary blotting procedure, and detected using a double antibody enzyme immunoassay. This method is capable of phenotyping 8 ng of GC extracted from bloodstains, a fourfold increase in sensitivity when compared to immunofixation and silverstaining. A total of 2424 casework bloodstains have been analysed and GC phenotypes identified in 78 percent of samples. The method is suitable for use in routine laboratories and is more sensitive than other methods for GC phenotyping of casework bloodstains. 2 tables, 5 figures and 15 references. (Publisher abstract)