OBJECT: The goal of this study was to examine the changes in body weight and glucose levels of the patients treated with risperidone, clozapine or haloperidol in order to compare the effect of risperidone or clozapine with that of haloperidol. METHODS: For nine months(January to September, 2003), a prospective study was performed in 60 patients with chronic schizophrenia who were in Seoul National Hospital. Two-week period was required for a drug wash-out. The patients were randomly assigned to risperidone, clozapine and haloperidol groups. They were given risperidone(n=20), clozapine(n=20) and haloperidol(n=20), respectively, everyday for 12 weeks. To examine the effects of these drugs on body weight and fasting glucose levels, we measured body weight and glucose levels of all the patients first without the drug treatment and at each end of 4, 8, and 12-week periods with the treatment. And we examined the differences among three groups in the changes of body weight and fasting glucose levels. RESULTS: There were no significant differences in the changes of the body weight and fasting glucose levels between the atypical antipsychotics(risperidone or clozapine) and the typical antipsychotics(haloperidol). CONCLUSION: The study in the patients with chronic schizophrenia suggests that risperidone or clozapine do not cause any additional effects on body weight or glucose levels compared to haloperidol.