Ionic fluxes are thought to he involved in mediating the prolifer-ation of peripheral blood lymphocytes (PBLs) in response to mitogenic substances^1,2. Among the earliest events occurring after the addition of mitogen to cultured lympocytes are changes in rates of cation transport^3–9. We were interested, therefore, in the possible role of ion channels in mediating the lymphocyte proliferative response. The development of patch clamp tech-niques by Neher and colleagues^10–12 has made it possible to study membrane conductances in a variety of small cell types¹². We have developed a method which uses monoclonal antibodies to make cells adhere to solid surfaces for two major reasons: (1) it is much easier to patch clamp stationary cells, and (2) the method can be used to selectively adhere a particular cell type from a heterogeneous population. We have used these techniques here to identify whole-cell potassium currents, in lymphocytes recognized by OKT11 monoclonal antibody, which are increased 1.9-fold by mitogenic stimulation.