Each immunoglobulin molecule consists of two identical heavy chains and two identical light chains. There are two types of light chains designated as kappa and lambda. The gene rearrangement process that generates the immunoglobulin molecule results in either a productive kappa gene or a productive lambda gene. The mechanics of the rearrangement process normally produce approximately twice as many kappa-bearing cells as lambda. However this ratio loses during malignant transformation. The kappa light chain antibody labels kappa light chain expressing B lymphocytes and plasma cells. Other cells may also express kappa light chain due to nonspecific uptake of immunoglobulin. Individual B cells express either kappa or lambda light chains. Monoclonality is generally assumed to be evidence of a malignant proliferation. Paired with lambda, kappa light chain is useful in identifying monoclonality of lymphoid malignancies. Anti-Kappa detects surface immunoglobulin on normal and neoplastic B-cells. In paraffin-embedded tissue, anti-kappa exhibits strong staining of kappa-positive plasma cells and cells that have absorbed exogenous immunoglobulins. When dealing with B-cell neoplasms, the determination of light chain ratios remains the centerpiece. Most B-cell lymphomas express either kappa or lambda light chains, whereas reactive proliferations display a mixture of kappa and lambda positive cells. If only a single light chain type is detected, a lymphoproliferative disorder exists. Monoclonality is determined by a kappa-lambda ratio of greater than or equal to 3:1 or a lambda-kappa ratio greater than 2:1. Tonsil is an appropriate control: Approximately half of the peripheral mantle zone B-cells must show a distinct membranous staining reaction for IgK, while the remaining mantle zone B-cells (which are IgL producing) should be unstained.