Sixty-five psychotic probands were divided into three groups (low, intermediate, and high) on the basis of the GH response to the dopamine receptor agonist apomorphine. Two hundred and sixty-five first-degree relatives of the probands were diagnosed according to SADS-DSM-III methods, and the relatives of the three groups of probands were compared so as to detect familial differences in the incidence of DSM-III Axis I disorders, schizotypal personality disorder, and antisocial personality. Although the morbid risk of schizophrenic spectrum disorder was only 3.1% in the relatives of the high GH probands, the morbid risk for disorders of the schizophrenic spectrum was 17.0% and 10.7% in the relatives of the intermediate and low GH probands, respectively. These data provide preliminary evidence that there may be a psychotic subtype that is characterized by supersensitivity of the dopamine system that is familially, and perhaps genetically, distinct from the bulk of the schizophrenias.