To investigate whether the abnormalities of antisaccades in schizophrenics could be explained by a dysfunction of the frontal cortex, we examined 10 patients with frontal cortical lesions and 22 patients with idiopathic Parkinson's disease with mild symptoms (Yahr I-II) using the same tasks, and compared the results with those obtained in schizophrenics. The frontal patients with lesions covering the frontal eye field and prefrontal cortex showed more errors, longer latencies, and lower peak velocities in the antisaccade task, despite giving normal results in the visually guided saccade task. This was similar to the results observed in schizophrenics. Parkinsonian patients did not consistently show a significant difference in the antisaccade task. These results indicate specific abnormalities of antisaccades in schizophrenics and patients with frontal cortical lesions but not consistently in Parkinsonian patients. This suggests that the abnormalities of antisaccades in schizophrenics might be explained by a frontal cortical dysfunction.