The authors provide the data on the dynamics of the hematological parameters during continuous leponex (clozapin) treatment of two group of patients treated in 1973-1989 at the All-Union Mental Health Research Center, USSR AMS (107 patients) and at 12 Research Centers of the USSR, CSFR, Bulgaria and Poland (642 patients). The mean duration of the treatment was 4.8 and 12.4 months respectively. Moderate leukopenia (3000-4000/ml) developed in 0.5 and 1.2% of all the analyses, the neutrophil/leukocyte ratio always remained within normal (50% and higher), whereas the neutrophil count did not drop below 1600/ml, i. e. it was not pathological. Despite the relatively long treatment no cases of granulocytopenia (or agranulocytosis) were recorded. It is shown that the side hematological effect is not related to the magnitude of the diurnal dose of leponex. Recommendations are given for wide use of leponex in medical practice under constant control of the blood status, with the use of the method of a slow and progressive augmentation of the daily dose.