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Two cases of multiple myeloma with IgA gammopathy and the syndrome of serum hyperviscosity are reported. A common feature of both patients was the production of large amounts of polymeric IgA (more than 50% of the monoclonal proteins existed as dimers or larger forms). However, similar large amounts of polymeric IgA were present in sera with only slightly raised viscosity, suggesting that factors such as the molecular configuration of the polymers or their sub-units may play a role in determining serum viscosity. The association of plasmapheresis and chemotherapy produced remarkable improvements of the symptoms attributable to increased serum viscosity, and 16 months after diagnosis one of the patients has survived relatively free of symptoms. The hyperviscosity syndrome is being diagnosed with increasing frequency in association with IgA multiple myeloma, and should be investigated in all cases with monoclonal proteins exceeding a concentration of 3-0 g/dl.

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