Electropolymerized poly(o-toluidine) (PoT) films in the fully reduced state were studied using in situ neutron reflectivity. Acquisition of specular reflectivity profiles (as a function of neutron momentum transfer) for films exposed to perchloric acid solutions using H2O and D2O as solvents ('contrast variation') allowed extraction of structural information. In particular, it was possible to determine the polymer and solvent volume fractions within the film as functions of distance perpendicular to the interface. The data fit a single homogeneous layer model with a diffuse outer polymer I solution interface. Within the interior of the film, the solvent volume fraction was small and varied with electrolyte composition. Film thickness increased monotonically with perchloric acid concentration: this was attributed to increased solvent content at low concentration and perchloric acid permeation at high concentration.