A series of 191 patients of bronchial asthma were treated with menaquinone for not less than one year, and the clinical effect of the drug was investigated. 1) The therapy with menaquinone only gave effective rate of 90.0% (a marked effective rate of 42.4%) in mild patients, an effective of 86.7% (a marked effective rate of 30.0%) in moderate patients, and an effective rate of 72.2% (a marked effective rate of 27.3%) in severe patients. namely, considerably high effective rates were attained by the therapy in the respective patients. 2) The therapy with menapuinone, in conjunction with hyposensitization therapy, gave an effective rate of 100% (a marked effective rate of 33.3%) in mild patient, and an effective rate of 93.8% (a marked effective rate of 34.4%) in moderate patients, but such a low effective rate as 60% (a marked effective rate of 10%) in severe patients. It was revealed that menaquinone therapy is more effective, when employed in conjunction with hyposensitization. 3) The double blind stuby of the clinical effects of menaquinon revealed that the placebo used in the study was effective on only 16.7% of the patients treated with it, and that the incidence of recurrence due to discontinuance of menaquinone therapy tended to be low in patients treated with the drug for long periods.