Seventy-five patients with bronchial asthma were treated with heparin by three different administration methods : 5000 u intravenously plus 5000 u by inhalation (method 1), 5000 u intravenously plus 5000 u by inhalation combined with 1 mg sulbutamol (method 2) and 10000 u by inhalation (method 3). The percent efficacy of heparin therapy was 44.4 % in the bronchial asthma patients treated by method 1, 72.7% in those treated by method 2 and 25.0% in those treated by method 3. Heparin therapy was more effective in patients over 50 years old, those with an age at onset of 40 years or more (late onset asthma) and those with serum IgE levels of less than 400 u/ml. The efficacy of heparin was also observed more frequently in cases with lower FEV1.0%, (V50) and (V25) values. Reduction of the plasma heparin concentration 1 h after intravenous administration was more rapid in cases in which heparin was effective than in those in which it was not.