Pan B-Cells is a monoclonal antibody directed against equine Ig light chains. Characterization studies demonstrated that Pan B-Cells bound 100% of CD5-ve peripheral blood lymphocytes and recognized all equine B-cells (Lunn et al. 1998) As the antigen recognized by Pan B-Cells appears to be present on the surface of all equine B-cells it is therefore is a reagent that can be used as a pan B-cell marker for domestic horses (Breathnach et al. 2005). Specific anti equine reagents have yet to be fully characterized for the typically recognized B-cell makers such as CD19, CD20, CD21, CD22 and CD79. While testing has demonstrated the cross reactivity of some monoclonal B-cell markers raised against other species with equine B cells, such as the CD79a antibody, an overview of which may be found in the report of the second equine leucocyte antigen workshop (Lunn et al. 1998). With specificity for equine Ig light chains, Pan B-Cells may be used to detect all equine immunoglobulin classes and subclasses in FLISA applications.