This study was designed to investigate the clinical safety of risperidone. The subjects consisted of 19 patients diagnosed as chronic schizophrenia with DSM-III-R, who had been admitted to the Taegu Catholic mental hospital from April 26, 1991 to December 19, 1991. After a wash-out period of 7 days, they were treated with risperidone for a period of 16 weeks unders single open condition. The mean dosage of risperidone administered to patients were 11.89土 4.59 mg per day. Blood pressure, heart rate, body weight, hematology, biochemistry, ECG were assessed : extrapyramidal symptoms were assessed by means of ESRS : other side effects were evaluated by UKU side effect rating scale. The results were as follows : 1) Among vital signs, changes of standing heart rate(P<C.05) and standing systolic blood pressure(P<.05) were significant, but these were within normal range. 2) A statistically significant increase was seen in body weight(P<0.00l). 3) Among the ESRS subscales, statistically significant decrease was seen in clinical global impression of severity of parkinsonism(P<C0.05). 4) Statistically significant changes were not found in blood chemistry, hematology, ECG and UKU side effect rating scale. The above results suggest that risperidone is clinically safe except for increased body weight