The studies were performed in 32 patients in the age range of 17-58 years suffering from bronchial asthma in the exacerbation period of their illness. 16 patients suffered from IgE related/atopic and 16 from IgE non IgE related/nonatopic bronchial asthma. The complement haemolytic activity (CH50) and the activity of C1 inhibitor (C1 INH) were measured in the plasma. In 60% of patients with IgE related asthma and in 45% of patients with non IgE related asthma we stated decrease of CH50. The activity of C1INH also was decreased in 80% of patients with atopic asthma and in 40% of patients with nonatopic asthma. The observed changes were not related to aspirin tolerance as well as to IgE mediation of their illness. Control examinations of these parameters repeated during remission of asthma symptoms in 11 patients with low values during the exacerbation of the illness (in 5 patients with atopic and in 6 with non-atopic asthma) revealed an increase of their values; however without features of normalisation.