Decanohydroxamic acid had almost no antibacterial activity. At 100 γ/ml, the acid showed growth inhibition on all the fungi tested except Monosporium apiospermum 213. The acid was found to have atropine-like, papaverine-like, anti-acetylcholine, and antihistamine actions, and a slight effect on blood (number of erythrocytes, leucocytes, and hemoglobin), but no marked effect was found on other factors. The action of this acid on the circulating system is mainly vasodilation and depression of the total carotid pressure, and no marked changes were produced in heart movement and cardiogram. A very slight irritation was observed as its local action, especially in an emulsified ointment on the skin, but not when the acid was used as a lipophilic ointment. Acute toxicity of the acid was very weak, the 2.5% Tween suspension giving the values of over 1430 mg/kg in mice by subcutaneous and intraperitoneal injection, over 7200 mg/kg in mice by oral administration.