The study was concerned with the dynamics of correlations between IgA, IgM and IgG levels involved in pigmented neoplasm development in 154 cancer patients and 75 healthy subjects. The dynamics was found to represent stages of tumor development rather than changes in absolute indexes of serum immunoglobulin concentrations. The nature of changes in the structure of correlations suggested a possible switch from IgM to IgG and IgM to IgA secretion, i.e. disturbances in B-lymphocyte differentiation. Said changes were observed at a certain stage of melanoma progression, namely, during metastatic spreading.