A simple test of smooth-pursuit eye movements disclosed a striking association between deviant eye tracking and clinically diagnosed schizophrenia. A high proportion of the schizophrenic patients' first-degree relatives who were not themselves clinically schizophrenic also showed deviant eye-tracking behavior. The relationship of poor eye tracking and schizophrenia is even stronger when specific psychological test evidence of thought disorder is used operationally to classify patients. The eye-tracking dysfunction may thus represent a genetic marker that can prove highly useful for studying the transmission of a vulnerability to schizophrenia. The findings suggest proprioceptive and interoceptive involvement in schizophrenic pathology.