To determine whether colchicine prevents or ameliorates amyloidosis in patients with familial Mediterranean fever, we followed 1070 patients with the latter disease for 4 to 11 years after they were advised to take colchicine to prevent febrile attacks. Overall, at the end of the study, the prevalence of nephropathy was one third of that in a study conducted before colchicine was used to treat familial Mediterranean fever. Among 960 patients who initially had no evidence of amyloidosis, proteinuria appeared in 4 who adhered to the prophylactic schedule and in 16 of 54 who admitted non-compliance. Life-table analysis showed that the cumulative rate of proteinuria was 1.7 percent (90 percent confidence limits, 0.0 and 11.3 percent) after 11 years in the compliant patients and 48.9 percent (18.8 and 79.0 percent) after 9 years in the noncompliant patients (P less than 0.0001). A total of 110 patients had overt nephropathy when they started to take colchicine. Among 86 patients who had proteinuria but not the nephrotic syndrome, proteinuria resolved in 5 and stabilized in 68 (for more than eight years in 40). Renal function deteriorated in 13 of the patients with proteinuria and in all of the 24 patients with the nephrotic syndrome or uremia. We conclude that colchicine prevented amyloidosis in our high-risk population and that it can prevent additional deterioration of renal function in patients with amyloidosis who have proteinuria but not the nephrotic syndrome.