Background: Primary localized cutaneous nodular amyloidosis (PLCNA) is a rare disease, and its pathogenesis of amyloid deposition is still unknown. Objective: The purpose of this study was to know the origin of amyloid in PLCNA. Methods: Water-soluble amyloid fibrils were isolated from the skin and resolved on SDS-PAGE, then subjected to immunoblot analysis. Results: The major amyloid fibril protein was a 29-kD peptide which reacted with both anti-λ- and anti-K-light-chain antibodies. Conclusion: Amyloids in this particular case of PLCNA are derived from the polyclonal immunoglobulin light chain and some cases of PLCNA could be reactive diseases rather than neoplastic ones.