Tissue and extractable metabolites from the subtropical gorgonianLeptogorgia virgulata (Coelenterata: Anthozoa: Octocorallia: Gorgonacea) induce vomiting in a variety of fish species. To elucidate the chemical bases of this phenomenon, experiments were undertaken with purified pukalide, a cembranoid diterpene that comprises as much as 0.1-0.5% of the wet tissue weight ofL. virgulata. When incorporated into artificial foods at concentrations corresponding to the levels found inL. virgulata, pukalide induced emesis when delivered orally to killifish (Fundulus heteroclitus). The threshold dose for pukalide-induced emesis was 0.05 mg/g fish body weight. Control pellets devoid of pukalide did not induce vomiting. The emetic effect of pukalide was dose-dependent, as fish ingesting more than 0.100 mg pukalide/ g body weight exhibited a significantly higher incidence of vomiting than fish ingesting lower doses of pukalide (G=5.5,df=1,P<0.025). The elapsed time between ingestion of pukalide-containing pellets and emesis was significantly longer in fish that ingested marginally emetic doses of pukalide (Kruskal-WallisH=4.00, significant withP<0.05). Although not markedly unpalatable to fish, pukalide may function in nature as a defensive toxin by inducing emesis and learned aversion in potential octocoral predators.