Current-time and steady state current behaviour were simulated for an ultramicrodisk electrode (UMDE) inlaid flush with an insulating plane and overlaid by a flat film of polymer containing an enzyme, of various film thicknesses and essentially infinite extent. Steady state currents go through a maximum for some film thickness H, and then approach a constant value for thicker films. This constant value is the same as that for the diffusion limited current at an UMDE in a semi-infinite medium. Response times to 95% of the steady state current, for thin films are shorter than can be achieved using a flat disk electrode and a hemispherical polymer drop, but for large Hthey are slightly longer for comparable film thicknesses/radii. A hemispherical electrode under a hemispherical polymer drop, however, behaves much like the present arrangement. (C) 2014 Elsevier Ltd. All rights reserved.