Both acquired and familial amyloid neuropathies carry a poor prognosis. In addition, amyloid is sometimes difficult to visualise in nerve biopsy specimens, and the pathogenesis of nerve lesions is still a matter of controversy. In order to learn more on the subject, we studied nerve specimens from seven patients with proven amyloid neuropathy by ultrastructural immunocytochemistry in order to better understand their pathogeny and to evaluate the reliability of the method for detection of amyloid antigens in the endoneurium. An indirect immunolabelling technique using protein A-gold complex (pA-g) was applied. Polyclonal antisera against human IgG, IgM, lambda and kappa light chains and prealbumin were assayed. Amyloid fibrils were labelled in six of seven cases: in four cases with anti-transthyretin (TTR) antibodies and in two with anti-lambda light chain antibodies. The type of immunolabelling correlated with the biochemical type of the amyloidosis as defined by TTR gene analysis and serum immunoelectrophoresis. The amyloid fibrils and gold labelling were always located in the endoneurial space. No intracellular deposit or labelling was found. The immunolabelling was highly specific, gold particles being detected only near to amyloid fibrils with no background gold labelling. Ultrastructural immunolabelling with pA-g could be used for detection of amyloid in progressive axonal neuropathy of unknown origin, with important therapeutic implications.