Mixtures of aqueous solutions of dextran and of poly(ethyleneglycol) form immiscible two-phase systems suitable for the separation (by partitioning) of cells based on subtle differences in their surface properties (Walter, H. (1977) in Methods of Cell Separation (Catsimpoolas, N., ed.), Vol. 1, pp. 307–354, Plenum Press, New York). Human peripheral blood lymphocytes were subjected to countercurrent distribution (a multiple-extraction procedure) in a charged phase system which yields fractions of cells enriched with respect to different surface markers (B-, T- and F c-receptor-bearing) and of different size (Walter, H., Webber, T.J., Michalski, J.P., McCombs, C.C., Moncla, B.J., Krob, E.J. and Graham, L.L. (1979) J. Immunol. 123, 1687–1695). The electrophoretic mobilities of cells in these fractions were measured by means of analytical particle electrophoresis (Bangham, A.D., Flemans, R., Heard, D.H. and Seaman, G.V.F. (1958) Nature 182, 642–644). The bulk of B-lymphocytes had not only the lowest partition coefficient (i.e., lowest affinity for the top, positively charged phase) but also the lowest electrophoretic mobility, T-lymphocytes had a higher partition coefficient and mobility, and the population comprising most of the F c-receptor-bearing and largest lymphocytes had the highest partition coefficient but an intermediate mobility. The lymphocytes with highest mobility resolved by countercurrent distribution have yet to be characterized. The results with large and F c receptor-bearing lymphocytes again emphasize that the charges measured by cell electrophoresis and by partitioning are not necessarily the same. They also have as an important, practical consequence that populations enriched with respect to F c-receptor-bearing lymphocytes should be obtainable by a simple one- or two-step extraction process.