BACKGROUND: Primary systemic amyloidosis is an uncommon disease characterized by the accumulation in vital organs of a fibrillar protein consisting of monoclonal light chains. METHODS: We treated 220 patients with biopsy-proved amyloidosis. The patients were randomly assigned to receive colchicine (72 patients), melphalan and prednisone (77), or melphalan, prednisone, and colchicine (71). They were stratified according to their chief clinical manifestations: renal disease (105 patients), cardiac involvement (46), peripheral neuropathy (19), or other (50). RESULTS: The median duration of survival after randomization was 8.5 months in the colchicine group, 18 months in the group assigned to melphalan and prednisone, and 17 months in the group assigned to melphalan, prednisone, and colchicine (P<0.001). Among patients who had a reduction in serum or urine monoclonal protein at 12 months, the overall length of survival was 50 months, whereas among those without a reduction at 12 months, the overall length of survival was 36 months (P=0.03). Thirty-four patients (15 percent) survived for five years or longer. CONCLUSIONS: Therapy with melphalan and prednisone results in objective responses and prolonged survival as compared with colchicine in patients with primary amyloidosis.