There are still uncertainties as to the mechanism of many pathological conditions, among them atopic diseases. It has been disclosed that NAT2 demonstrates genetic polymorphism and that the rate of acetylation catalyzed by this enzyme varies from subject to subject. The rate of acetylation appears to be an independent variable, specific for a given individual, genetically determined and associated with a dysfunction of the immune system. Therefore it is an important determinant of atopic diseases. So far, the NAT2* genotype has not been studied in patients with atopy and the results of some investigations on the rate of acetylation in allergy remain equivocal. The aim of this work was to evaluate the frequency of the NAT2* genotype in children with atopic diseases, particularly bronchial asthma, in their first-degree relatives and in healthy children. Furthermore, it was decided to check whether the NAT2* genotype may serve as a predispositing factor to atopy and whether the acetylation polymorphism is associated with the clinical course of these diseases. The study was performed in 266 children, including 85 patients with atopy and 181 healthy controls. Genomic DNA was isolated from peripheral blood and the NAT2* genotype was determined using PCR and restrictase digestion. The results shows that the NAT2* genotype, which is characteristic of slow acetylation, is an important risk factor in atopy, particularly bronchial asthma. A link between the clinical course of atopy and slow acetylation has been suggested.