The monitoring system LEX-SYS was introduced in the Czech Republic in 1993. Annually 200–250 new patients are included into this system. Values of leukocytes and neutrophil granulocytes are regularly monitored in these patients. These values are monitoring weekly during the first 18 weeks of treatment, and then monthly until withdrawal of the drug. Till the middle of May 2001 1737 patients were included in this database. During 7 years of this monitoring system 7 cases of agranulocytosis (0.4 %) were observed granulocytopenia in 36 cases (2,1 % of all included patients). There was no connection between the dose and patients age. The majority of haematological side effects during the first 18 months. Nevertheless even the rest of the 34 % cases lead us to the conviction about the neccesity of further monitoring of the blood count. In total database there was no case of letal agranulocytosis in the monitored patients.

        Key words: agranulocytoses, monitoring system LEX-SYS, clozapine, leukocytes.