Conditions in which lymphadenopathy is associated with dysgammaglobulinemia may be divided into two groups: those in which etiologic factors and pathogenesis are well established, and those which are still a medical dilemma. Only a few belong to the former group: infections, immunizations, and drug-induced conditions being the best examples. Unfortunately, the great majority belong to the latter group. Interestingly enough, many conditions with lymphadenopathy and dysgammaglobulinemia share similar histologic features, such as infiltration with lymphocytes, immunoblasts, plasma cells, and histiocytes. This pleomorphic infiltration may appear together with prominent vascular proliferation. In animal experiments, angiogenesis was induced by administration of immunocompetent lymphocytes into the skin of unimmunized, irradiated mice. Therefore such lymphocyte-induced angiogenesis may be a manifestation of the graft-versus-host reaction. Recent developments in immunology, such as the discovery of many membranous markers and receptors on the lymphocyte membrane, the study of cytoplasmic structure and synthetic products, detection of enzymatic aberrations and chromosomal abnormalities, and refinement in histochemical techniques, have led to attempt to reclassify lymphoplasmacytic and leukemic disorders. Indeed, several classifications coming from different coutries and from various centers in the same country have been proposed, leading to a typical "Tower of Babel" phenomenon. It is obvious that more knowledge of etiologic factors and pathogenetic mechanisms is necessary to classify, cure, and eventually prevent the diseases described in this paper.