Subclasses of 176 IgG and 62 IgA myeloma proteins were determined by indirect ELISA with monoclonal antibodies, as well as by an immunoblotting technique (for monoclonal IgG) and by immunoelectrophoresis against the lectin jacalin (for IgA). The subclass distribution of monoclonal IgG did not reflect mean normal serum levels of the correspondent isotypes, with an over-representation of IgG1 and IgG4 and an under-representation of IgG2 and IgG3 in myeloma. Similarly, IgA2 myeloma were clearly under-represented.