A theoretical expression is presented which includes the effect of IR drop on the current response following a potential step. The expression is valid for reversible and irreversible simple heterogeneous electron transfer under planar diffusion conditions. The introduction of uncompensated resistance in the model enables calculation of a theoretically correct chronoamperometric response. Curve shapes in related voltammetric techniques such as normal pulse voltammetry are easily derived. The theoretical chronoamperometric and normal pulse voltammetric responses are verified experimentally.