Pharmacological properties of a substance extracted from the roots of Miconia sp. (Herb. I.A.U.F.Pe-1903) named as primin (2-metoxi-6-n-pentil-benzoquinone), are described. Median lethal dose was evaluated in 12.78 mg/kg, intraperitoneally, by Thompson and Weil method. Local irritation on rat skin and rabbit vascular endothelium, were positive. In doses up to 8 mg/kg it did not affect rat respiratory mechanism. Primin (1 mg) induced to decrease the dropping of a nutrient flux through isolated peribronchial tissue. Normal flux was obtained when adrenalin (100 mcg) was administered. Urinary excretion and blood level of this substance, was detected by microbiological method, after the fourth and the fifth hour of the drug application. Doses of 1 and 3 mg/kg i.p. were tested.