The modulation of auditory input processing in relation to slow event-related potentials was examined in two studies. A steady-state response (SSR) was evoked by a stimulus train delivered at 40 Hz. Slow potentials were elicited by an oddball task implemented as changes in the pitch of single stimuli within this 40-Hz train. In study 1, subjects responded to rare targets by means of a button press. In study 2, subjects responded to targets by means of a motor response in one session and by silent counting in another session. In both studies, the oddball task elicited a P300 to targets. SSR amplitude was reduced 100 ms following each stimulus, while a second amplitude reduction around 350-400 ms was discovered following targets, in particular, following a button press. Parallel to SSR amplitude reductions, the latencies between stimulus and subsequent SSR peak were reduced. Results indicate that processing of oddball stimuli and motor responding alters 'automatic' auditory processing at the level of the primary auditory cortex; the second SSR amplitude reduction which develops in parallel to P300 might support the hypothesis that slow positive potentials indicate widespread (disfacilitation) inhibition of cortical neural excitability.