Several investigators have studied Helianthus annuus L. (Fam. Compositae) in a search for novel antimicrobial agents. Chlorogenic acid (l), isochlorogenic acid (2), and annuithrin (3) have been so identified previously. In addition, because of its commercial importance and botanical prominence, several recent phytochemical studies of the Helianthae have also been carried out (4- 6). We wish to report that the stems of Helianthus annuus collected in Douglas County, Kansas, in the fall of 1979- 198 1 were subjected to bioassay-directed fractionation (7) and gave small quantities of trachyloban- 19-oic (8,9) and (-)-kaur- 16-en-19-oic (9,lO) acids as active antimicrobial constituents. Interestingly, the same two acids have recently been shown to be responsible for resistance of some strains of sunflower to the sunflower moth (Homoeosoma electellum) (1 1). (-)-Kaur- 16-en- 19-oic acid has also been isolated as an antimicrobial agent from Croton argyropbylloides ( 16) and Minania monagasensis (17).