Event-related brain potentials (ERPs) are altered in patients with a variety of psychiatric disorders and may represent quantitative correlates of disease liability that are more amenable to genetic analysis than disease status itself. Estimates of heritability are presented for amplitude and latency of the N1 and P3 components of the ERP measured at 19 scalp locations in response to visual and auditory stimuli for 604 individuals in 100 pedigrees ascertained as part of the Collaborative Study on the Genetics of Alcoholism. Significant heritabilities were found for visual P3 amplitude in response to all stimuli and for visual P3 latency in response to target and novel, but not nontarget, stimuli. Heritability of visual N1 latencies was uniformly low, whereas heritability of visual N1 amplitude was significant for all electrodes in response to the nontarget stimuli but only for posterior electrodes in the other two stimulus conditions. Heritabilities for auditory target P3 were similar to those of the visual stimuli, with auditory target P3 amplitudes and latencies both demonstrating significant heritability. For auditory P2 in response to non-target stimuli, peak amplitude was heritable, but latency was not. Auditory N1 amplitude and latency were significantly heritable for both target and non-target conditions and did not demonstrate the anterior/posterior pattern-ing obtained for visual N1 amplitude. This study represents the first systematic assessment of heritability of these potential neurophysiological markers in families with a history of alcoholism and suggests that many of these ERP phenotypes have heritabilities strong enough to justify genomic screening for loci jointly influencing ERP abnormalities and liability to alcoholism.