Objective:To evaluate the pharmacokinetics of clozapine in the first episode and drug naive schizophrenia or schizophreniform psychosis and the relationship between the blood level of clozapine and the efficacy or side effects. Method:Twenty eight patients which never been used antipsychotic drugs were entered into the study. The first 50mg oral dose of clozapine was given after fasting for 12 hours. Blood samples were taken at 0 5,2,5,8,12,24 and 36 hours after giving clozapine to measure it's blood level and calculate the parameters, then used pharmacokinetic parameters to get the predictable dosage of clozapine. We compared the effects and side effects between the patients using less than predictable dosage and more than it, and the efficacy and side effects were also compared between the patients whose clozapine blood levels were in the range of 200~600ng/ml and out of this range, in addition, we compared the blood levels, dosage, total scores of side effects according to EEG. Results:The half life of absorption phase and elimination phase were 1 13 hr and 9 50 hr respectively, plasma peak concentration reached at 3 44 hr. After 4 weeks, no significant differences were founded in blood levels of clozapine and the dosage that patients taking actually between different predictable dosage groups. Conclusion:The side effects of clozapine (eg. abnormal EEG) is associated with it's increase of blood level.