Amyloidosis is the extracellular deposition of normally soluble autologous protein in a characteristic abnormal fibrillar form. Systemic amyloidosis and some local forms are progressive, cause major morbidity, and are often fatal. No treatment specifically causes the resolution of amyloid deposits, but therapy that reduces the supply of amyloid fibril precursor proteins can improve survival and preserve organ function. Major regression of amyloid occurs in at least a proportion of such cases, suggesting that the clinical improvement reflects mobilization of amyloid. The clearest evidence for regression of amyloid has been obtained in juvenile rheumatoid arthritis patients with AA amyloidosis treated with chlorambucil. This drug suppresses the acute phase production of serum amyloid A protein, the precursor of AA amyloid fibrils, and is associated with remission of proteinuria and greatly improved survival. In many such patients, scintigraphy with serum amyloid P component shows major regression of amyloid over 12 to 36 months and frequently reveals a discrepancy between the local amyloid load and organ dysfunction. Measurement of target organ function is therefore not an adequate method for monitoring treatment aimed at promoting the resolution of amyloid. In monoclonal immunoglobulin light chain (AL) amyloidosis the aim of treatment is to suppress the underlying B-cell clone and, therefore, production of the amyloid fibril precursor protein. This can be difficult to achieve or sustain and, since the prognosis is so poor, many patients die before benefits of therapy are realized. A recent development has been the introduction of liver transplantation as treatment for familial amyloid polyneuropathy caused by transthyretin gene mutations. This leads to the disappearance of variant transthyretin from the plasma and halts progression of the neurologic disease. Features of autonomic neuropathy frequently ameliorate, and improvement in peripheral motor nerve function has been recently reported. Serum amyloid P component scans show regression of associated visceral amyloidosis. This surgical form of gene therapy holds much promise for patients with familial amyloid polyneuropathy and has been widely adopted. The only other form of amyloidosis in which the supply of the fibril precursor protein can be sharply reduced is beta 2M amyloidosis in long-term hemodialysis patients. Renal transplantation lowers the plasma concentration of beta 2M to normal levels and is associated with rapid improvement of the osteoarticular symptoms. Preliminary observations suggest that the beta 2M amyloid deposits also can regress in some patients.(ABSTRACT TRUNCATED AT 400 WORDS)