In this study, a cohort of 109 patients with multiple myeloma were followed prospectively. Eight patients (7%) were found to have biclonal M component, an occurrence rate considerably higher than that reported in literature. Biclonal myelomas were compared with the other monoclonal variants of myeloma by a number of biologic, clinical, immunological, biochemical, roentgenological, therapeutical and prognostic parameters. Among the biclonal myeloma patients there was strong male predominance, higher frequency of patients in advanced stage of the disease, combined production of predominantly kappa light chains, hypoalbuminemia and thrombocytopenia. Their response to therapy did not differ from that of the patients with monoclonal myeloma variants. The median survival of patients with biclonal myelomas was 25 months, ranking third by shortened survival after patients with light chain and D-type myelomas.