The aetiology, clinical course and affected organs were studied in 124 patients with acquired systemic amyloidosis and seven patients with organ-limited amyloid deposits. Seventy-five patients had reactive systemic AA amyloidosis, which was associated with rheumatic disease in 55 and with chronic infection in 13 cases. Forty-nine patients had systemic AL amyloidosis. Thirteen of these cases were associated with myelomatosis and 11 with non-malignant immunocyte dyscrasias. In 25 patients with systemic AL disease no immunocyte dyscrasia was identified. Renal involvement dominated the clinical course of both forms of systemic amyloidosis, and renal failure was the most common cause of death. Gastrointestinal disturbance and hepatosplenomegaly were found in both AA and AL disease, although differences were noted in the distribution of amyloid protein within rectal biopsies. Amyloid cardiomyopathy, neuropathy and macroglossia were present in patients with AL amyloidosis only. These clinical patterns were reflected by tissue distribution at necropsy in 67 patients.