Attentional abnormalities have long been known to characterize patients with schizophrenia. The data discussed in this report suggest that impaired attention (at least as measured by a specific task, the Continuous Performance Test, Identical Pairs (CPT-IP) version) may also be an endophenotype of particular promise for use in molecular genetic studies of schizophrenia. This conclusion is based on findings indicating that the deficits in verbal and spatial attentional processing tapped by the CPT-IP are heritable, developmentally stable, independent of clinical state, and predict future spectrum disorders in the at-risk offspring of parents with schizophrenia.