A pungent isobutylamide of an unsaturated C18 acid has been isolated from the roots of Heliopsis scabra Dunal. The substance, for which the name "scabrin" is proposed, is appreciably more toxic than the pyrethrins to house flies. Hydrogenation of the amide gave N-isobutylstearamide, and on oxidation it yielded butyric, oxalic, succinic and N-isobutyloxamic acids. On the basis of these degradations and of its ultraviolet absorption spectrum, scabrin was shown to be the N-isobutylamide of either 2,4,8,10,14-, 2,4,8,12,14-, 2,6,8,10,14- or 2,6,10,12,14-octadecapentaenoic acid, or a mixture of these isomers. Also isolated from the roots were two crystalline compounds, and a fluorescent oil which is also considerably toxic to house flies. These compounds will be investigated further.