Many schizophrenia patients show degraded detection of coherent motion. This visual deficit may (1) be a consequence of having a specifically schizophrenic psychosis, (2) be a non-specific effect of suffering from a severe illness (i.e., "generalized deficit"), or (3) reflect properties of the visual motion processing system that play an antecedent, possibly causal role in the pathophysiology of a disposition to schizophrenia. To distinguish among these possibilities, we measured the accuracy of detecting the direction of coherent motion in 29 schizophrenia patients, 20 first-degree relatives of schizophrenia patients, 19 patients with bipolar disorder and 33 normal controls. The task requires the integration of dynamic signals from stochastic random dot patterns in order to discern the direction of their motion. Schizophrenia patients, as a group, showed significantly elevated thresholds for detecting the direction of coherent motion, but relatives of schizophrenia patients and patients with bipolar disorder did not differ from normal controls on this task. The results indicate that visual motion integration, normally mediated in motion-sensitive brain areas such as the Middle Temporal Area, is impaired in patients with a clinically manifest schizophrenic psychosis, but is intact in patients with a non-schizophrenic psychosis (bipolar disorder) and in the relatives of schizophrenia patients. Our findings suggest that deficiencies in integrating motion signals, while specific for schizophrenia, do not seem to be a co-familial trait.