Serum immunoglobulin levels IgG, IgA, IgM were assayed by laser-nephelometry and IgD by a liquid phase radio-immunoassay in 133 patients with monoclonal gammopathy. Our result show that IgD concentration decrease in parallel with polyclonal immunoglobulin levels. We observe a decrease of IgD level, more pronounced in malignant gammopathy in which the polyclonal immunoglobulin levels are usually low.