Serological test systems were established for determining the heavy-chain variable region (Vh) subgroups of immunoglobulin heavy chains. Myeloma proteins with known Vh subgroups based on amino acid sequence were utilized as the primary basis of reference for analysis by hemagglutination and hemagglutination inhibition. Good agreement between the chemical and serological typing was obtained and nonoverlapping systems established for the three major Vh subgroups. In a survey of 167 myeloma proteins, all except two were exclusively positive in one of the three systems. The two exceptions may represent a fourth subgroup. There was an overall incidence ratio of 1:2:3 for VhI:VhII:VhIII subgroups. Some differences in the overall ratios were encountered within the immunoglobulin classes. Certain advantages of the serological typing antisera were discussed with special emphasis on their use for studies of Vh antigens on the membranes of lymphocytes.