Through previous research, promising biological markers for schizophrenia have been identified. Abnormalities in eye movement, electrodermal activity, event-related brain potentials, attention and informational processing, and brain imaging have been reported. Studies of potential trait markers suffer from the lack of a standardized methodology, which makes comparisons of their results difficult. No one possible marker appears specific for schizophrenia. Additional studies in high-risk children and adults are needed using multiple measurements to define biologic similarities and differences between psychiatric syndromes in order to develop definitive trait markers for schizophrenia. Sufficient evidence does not exist to support the inclusion of biological markers among the DSM-IV criteria for schizophrenia, although some are sufficiently robust to merit mention among the associated features discussed in the text.