Whether the response to chemotherapy is a prognosticator in multiple myeloma (MM) is still not known. Therefore, the relationship between survival and the rate of monoclonal protein (M-protein) decrement during the first cycles of therapy was prospectively assessed in 262 patients with newly diagnosed MM that were included in a phase III trial (HOVON-16). M-proteins were collected monthly during melphalan-prednisone therapy (MP: melphalan 0.25 mg/kg, prednisone 1.0 mg/kg orally for 5 d every 4 weeks). Patients with light chain disease (n = 18), immunoglobulin M (IgM)-MM (n = 1) and no immunotyping (n = 1) were excluded. Of the 242 patients studied, 75% had IgG M-protein and 25% IgA; MM stages: I: 1%, II: 35% and III: 64%. The median M-protein decrease after the first cycle of MP was 21% for IgG and 27% for IgA, and declined to < 5% after four cycles. An obvious survival advantage was seen for patients who had an M-protein decrease of at least 30% after the first MP cycle, which became significant when an M-protein decrease of 40% or more was reached. As established prognostic parameters (Salmon & Durie stage, serum creatinine, and haemoglobin) also remained prognostically significant, we concluded that early response to MP predicts for survival in MM.