To understand a mechanism of underlying cognitive deficit in schizophrenia, the risk factors, cognitive function, blood dopamine concentrations and glutamate dehydrogenase activities of male schizophrenics with tardive dyskinesia(N=30) were compared with those of schizophrenics without tardive dyskinesia(N=30). The results were as following ; 1) The age, duration of illness and duration of medication were significantly more in schizophrenics with tardive dyskinesia than schizophrenics without tardive dyskinesia(respectively p<0.005, p<0.0001, p<0.0001). 2) The scores of MMSE, TIQ, VIQ and PIQ were significantly lower in schizophrenics with tardive dyskinesia than schizophrenics without tardive dyskinesia (rspectively p<0.0001). 3) Plasma dopamine concentrations were tended to be higher, and serum glutamate dehydrogenase activities were tended to be lower in schiz-ophrenics with tardive dyskinesia than schizophrenics without tardive dyskinesia. 4) The cognitive deficit seemed to be negatively correlated with duration of illness and duration of medication(respectively ${gamma}$=-0.496, ${gamma}$=-0.615).