Various C6 protein allotypes were examined using polyacrylamide gel isoelectric focusing followed by immunoblotting or hemolytic overlay. For several 'difficult' allotypes, neuraminidase treatment of samples and long-distance isoelectric focusing gels were applied. Nineteen different allotypes were distinguished besides the two common allotypes C6 A and C6 B. They were designated basically according to the previous statement on C6 nomenclature [Mauff et al., 1980].