Amyloid deposition in the quadriceps femoris muscle was investigated in 12 cases of systemic amyloidosis including 6 of AL-(primary or myeloma-associated) type, 2 of AA- (secondary) type, and 4 of prealbumin- (familial or sporadic) types. Clinically, muscle weakness was found in 7 patients. Among the 7 patients, one of the AL-type suffered from systemic myopathy showing progressive muscular stiffness, pseudohypertrophy, and weakness. The other 6 presented with polyneuropathy. Pathologically, no amyloid was found to be deposited in the AA-type. In all of the AL- and prealbumin-types, amyloid deposition was found in the blood vessels and peri- and endomysium. The degrees of amyloid deposition were marked in one case of the AL-type, which was considered to be suffering from amyloid myopathy, moderate in one of the AL-type, and slight in the rest of the AL-type and all of the prealbumin-type. Our observations and descriptions in the literature indicate that the presence and degrees of amyloid deposition in the skeletal muscles would be related to the types of amyloid proteins in amyloidosis. It seems likely that the affinity of amyloid to the skeletal muscles is variable in AL-type, probably depending on the molecular heterogeneity of AL protein, is low in prealbumin-type, and is almost absent in AA-type.