Abstract: A compound was isolated by fractionation of methylene chloride extract of the caulis of Sargentodoxa cuneata (Oliv) Rehd et Wils. On the basis of its melting point, rotational value, and spectroscopic data, it was identified as (+)-dihydroguaiaretic acid. It was shown to have antagonist activity toward platelet activating factor. This is the first evidence for the natural occurrence of an (+) optically active form of dihydroguaiaretic acid.