A case of isolated lambda-light chain proteinemia and proteinuria is reported. During a 42-month follow-up, no sign of myelomatosis or amyloidosis developed and Bence Jones proteinuria remained nearly of the same magnitude. This case of apparently idiopathic Bence Jones gammopathy, the first lambda-type so far reported, is added to similar observations to give further support to the contention that a benign counterparty to light-chain myeloma may exist.