Two-dimensional gel electrophoresis (2-DGE) associated with a very sensitive silver staining is one of the most powerful technique available for protein analysis. Proteins are separated in the first dimension by isoelectric focusing in a pH gradient, and in the second dimension by polyacrylamide gel electrophoresis. Proteins are thus separated according to their charge and to their size. The high resolution of 2-DGE allows the analysis of complex mixture of proteins with a great reproducibility. More than hundred different proteins can be individualized after 2-DGE of plasma or serum samples. Using this technique, we analysed samples obtained from normal donors and from patients with different gammopathies. Our results confirm that the heavy chains of immunoglobulins are easily detected and that the alpha, gamma and mu chains are clearly differentiated from one another. The typical polyclonal heavy and light chains appear as indiscrete spots after staining of the gels. On the contrary, the monoclonal chains appear as discrete spots. Monoclonal heavy chains have a restricted charge heterogeneity. We also analysed cold agglutinins, partially purified from plasma of three patients showing evidence of chronic hemolysis, a positive direct antiglobulin test of the complement type and anti-I autoantibodies. The 2-DGE have clearly demonstrated that these cold agglutinins were monoclonal IgM, when these later were not detectable by immunofixation electrophoresis. We think that the 2-DGE is a very usefull specialized aid to the analysis of such particular immunohematological problems.