Recent studies have established that amyloid fibrils found in different clinical conditions differ in the nature of their constituent proteins. In primary amyloidosis and in amyloidosis associated with multiple myeloma or macroglobulinaemia the amyloid fibrils are usually largely composed of fragments of immunoglobulin light chains. In secondary amyloidosis, protein AA, a unique protein unrelated to immunoglobulins, is the major component of the fibrils. Other chemical types of amyloid have been described in primary medullary carcinoma of the thyroid and in senile cardiac amyloidosis. In Papua New Guinea amyloidosis is seen secondary to chronic infections such as leprosy and tuberculosis as well as in patients without an apparent predisposing disease. The amyloid proteins obtained from a representative range of Papua New Guinean patients have been characterised and in all cases examined the amyloid was found to be of the protein AA or secondary type. Current research into the pathogenesis of secondary amyloidosis centres on the mechanisms whereby protein AA is derived from the presumed precursor molecule, protein SAA, which is a normal acute-phase reactant.