A biochemical study of three patients with clinical symptoms of Gaucher disease was carried out. Two of them had a significant deficiency of beta-glucocerebrosidase activity (a primary enzyme defect) in leukocytes and an enormous increasing of chitotriosidase activity in blood plasma that confirmed the diagnosis of Gaucher disease. Some differences in stability of mutant enzymes were found in these two cases. Mutation analysis revealed two point mutations--N370S and L444P in beta-glucocerebrosidase gene of both patients. Correlation between clinical picture, peculiarities of enzymatic defect and genetic status of patients is discussed. The influence of some epigenetic factors on phenotypic manifestation of the disease is supposed.