Auditory event-related potentials (ERPs) from a multidimensional selective attention task were recorded from 10 unmedicated schizophrenic patients and 10 age- and sex-matched healthy controls. Tone pip stimuli varying on the dimensions of pitch (high or low) and location (left or right ear) formed four 'channels' of stimuli: left low, left high, right low, and right high. The pitch difference was considerably more difficult to discriminate than the location difference. Subjects were instructed to pay attention to a designated channel and press a button whenever they detected a long-duration, rare target tone that occurred amongst frequent short-duration standard tones. There were a number of differences between unmedicated schizophrenics and controls in processing negativity elicited by standard tones. There was no evidence of hierarchical processing of stimulus dimensions in the early processing negativity component, and the late frontal component was virtually absent in schizophrenics. Furthermore, there was evidence that in schizophrenics the processing of the location dimension was delayed for standard tones having the same pitch as the target. The P300 component to attended target tones was substantially reduced in schizophrenics over parietal sites but there was no difference between the two groups over frontal sites. The results are interpreted in terms of multiple attentional deficits in schizophrenics that are indicative of a failure in the planning and execution of selective listening strategies. Such a failure may result from a dysfunction in the prefrontal regions of the brain.