A hybrid of the techniques of cellular adhesion chromatography and field-flow fractionation has been used for the effective separation of rat mesenteric B and T lymphocytes with nearly complete recovery of both cell species. Use of this hybrid technique also allows the relative binding strengths of cells to biomaterials and other surfaces to be rapidly and simply estimated. For the copolymer surface used here, B cells appear to bind with a force five times greater than T cells.