Anti-Lambda recognizes surface immunoglobulin on normal and neoplastic B cells. Anti-Lambda staining can be observed in B-cell follicles of human lymphoid tissue. In B-cell neoplasia, determination of light chain ratios continues to be helpful. Most B-cell lymphomas express either kappa or lambda light chains, whereas reactive proliferations show a mixture of kappa- and lambda-positive cells. If only one type of light chain is detected, a lymphoproliferative disease is very likely.