Monoclonal immunoglobulins (= paraproteins) in zone electrophoretic separation on paper, cellulose acetate foil or agar are demonstrated as narrow base gradients, which refers to the homogeneity of the molecules of the immunoglobulins. In unselected population they are observed in 0.1 to 1.2%, in which cases they more frequently appear with growing age, in persons older than 70 years they were established in 3%. The cause in question is only in a small part a plasmocytoma or another lymphoreticular disease. In the majority of cases, particularly in the cases with insignificant concentration of M-gradients the appearance of monoclonal immunoglobulins is the only deviation from the normal in an examination, which led to the notion essential benign monoclonal gammapathy. A therapy of this benign gammapathy is not necessary. For the demarcation of an early form of a plasmocytoma long-term controls with measuring of the concentration of the monoclonal immunoglobulin shall be carried out, since a permanent increase of the paraproteinaemia is the most reliable sign of a malignant gammapathy. Clinical observation and experimental investigations on animals make probable that the causes for the appearance of a benign monoclonal gammapathy are to be traced back to a special antigen stimulation in genetic disposition.