The conductive properties of a polyaniline film on a platinum electrode in sulfuric acid solutions have been studied using the current response to a light flash perturbation. For polyaniline in an insulating state, short-lived photocurrents were observed which lasted no longer than the light from the flash-unit itself, (first order decay constant (tau) less than 1.5 ms). For polyaniline in a conductive state, longer-lasting photocurrents were observed, (tau > 1.5ms), which provided an immediate indicator of regions of enhanced conductivity. Prolonged photocurrents indicative of high conductivity were observed up to a pH of 3.7, beyond which only shorter transients were obtained, consistent with previous polyaniline conductivity studies. The transition from conducting to insulating regions at more positive potentials was marked by the appearance of a short-lived cathodic photoresponse in place of a prolonged anodic photocurrent. This transition occurred at more positive potentials as the pH was lowered. Light of wavelengths longer than 600 nm still produced a significant photocurrent. Two models are proposed to account for the photocurrents when polyaniline is in an insulating and a conductive state.