An unusual triclonal IgG combination in the serum of a 56‐year old male with clinical stage IIIB multiple myeloma is reported. The patient initially had an IgG4(Λ) monoclonal protein in his serum and later developed an IgG2(κ) and an IgG (κ) which possessed the characteristics of both IgG1 and IgG3 subclasses with an unusual combination of allotypic markers. Three M‐proteins did not share idiotypic determinants. A rare class‐switch recombination followed by mutation has been considered as a possible mechanism leading to this combination.

No abstract