The mechanism of action of the drug was investigated from various points of view. The findings may be summarized as follows: 1. In the experiments of the degranulation of mesenteric mast cells of rats, menaquinone proved to significantly inhibit the degranulation either in active or passive sensitization with the reagin-like antibody. 2. Menaquinone did not inhibit the formation of the reagin-like antibody. 3. In the experiements of the degranulation of basophilic granulocytes from patients of bronchial asthma, the rate of appearance of A form basophilic cells upon addition of the antihuman IgE goat serum was not markedly but significantly inhibited in the patients treated with menaquinone for long periods, as compared with that in the control, whereas the in vitro addition of menaquinone did not exert a significant inhibitory action.</p
