Anti-HIV bioassay-guided fractionation of an organic extract of Ochanostachys amentacea provided an HIV-inhibitory polyacetylenic acid. The identity of this compound was established as (-)-17-hydroxy-9,11,13,15-octadecatetraynoic acid (1), also known as minquartynoic acid, by comparison of its physical and spectral data with previously reported values. Analysis of Mosher's ester derivatives of the methyl ester of 1 allowed assignment of S absolute stereochemistry to the lone chiral center. In an in vitro XTT-based anti-HIV assay, 2-5 micrograms/mL of minquartynoic acid (1) effectively inhibited human lymphoblastoid cell killing by HIV-1.