The exact analytical solution of the steady-state diffusion and first-order surface reaction at a cell wall chemoreceptor site is presented. Following Berg (Random Walks in Biology, Princeton Press, Princeton, NJ, 1983) and others, the receptor is modeled as a chemically active circular site on an impermeable, inert cell wall. Reaction rate currents to the receptor site are generated over the full range from the diffusion- to the chemical reaction-control limits. The exact form of the receptor site reaction rate current Is compared with the approximation (Lauffenburger and Linderman, Receptors, Oxford Univ. Press, Oxford, 1993) currently used of the series addition of the diffusion- and chemical reaction-control limiting rate expressions.