A series of 21 patients with multiple myeloma and a survival of more than 5 years was compared to another series of 70 cases of myeloma, which all died within less than 5 years. The statistical analysis of these two groups revealed six factors with a significant prognostic value. The population with a long term survival presented: a low incidence of large tumour masses (stage III according to Durie and Salmon's classification): 24 per cent compared with 72 per cent p less than 0.01); a frequency on asymptomatic or minimally symptomatic forms of 29 per cent versus 7 per cent in the control series (p less than 0.001); a haemoglobin level of 7.3 mmol/l versus 6.4 mmol/l (p less than 0.01); a low beta-2-microglobulin level (4 mg/l versus 11 mg/l) (p less than 0.02); a usually normal serum creatinine level (p less than 0.05). Retrospectively, the authors also observed that the response to treatment constituted an essential prognostic factor (69 per cent response compared with 20 per cent) (p less than 0.001). The serum calcium, the immunological type, the level of monoclonal component and the marrow plasmocytosis did not differ between the two groups. The authors consider all of these parameters, together with the calcitonin hypocalcaemia test to be useful in three situations: the therapeutic decision in minimally symptomatic patients, the choice between single agent or combination chemotherapy, the establishment of criteria of remission and suspension of treatment.