A group of 193 multiple myeloma (MM) patients consisting of cases treated only symptomatically (1959-63) or by nonsystematic monotherapy with Cyclophosphamide or Melphalan (1963-76) and of a subgroup given systematic polychemotherapy and intensive supportive treatment (1976-84) were evaluated for the practical applicability and prognostic relevance of three staging systems. The clinical staging system of Durie and Salmon and the quantitative system of Salmon and Wampler have proved in both subgroups of various periods and with different therapeutic approaches to be well applicable in the clinic allowing the patients to be divided into three prognostically different groups according to the size of the tumor mass. Merlini, Waldenström and Jayakar's staging system has likewise shown relationship to prognosis though the patients could be divided only into two prognostically different groups. It is evident that a deeper knowledge of MM requires nowadays a more comprehensive, complex and prognostically more relevant classification system.