Diffusion-limited voltammetric currents for the 1-e(-) reduction of nitrobenzene (NB) in acetonitrile (AN) over the entire composition range (0 less than or equal to x(NB) less than or equal to 1, x(NB) mole fraction of NE) were analyzed employing the Cullinan-Vignes equation to describe the interdiffusion of the redox species and solvent. Activity-corrected mutual diffusion coefficients at 45 degrees C were computed from isothermal liquid-vapor equilibrium data and steady-state limiting currents, I-lim, for NE reduction at a 12.5 mu m-radius Pt microdisk electrode. Application of activity-corrected mutual diffusivities in the Cullinan-Vignes equation appears to account properly for non-ideal behavior of I-lim for x(NB) > similar to 0.4. Values of I-lim are ’over-corrected’ by activity data to a small extent for x(NB) < 0.4, suggesting the self-association (i.e., clustering) of solution components.