Six Eurasian species of Carduus thistles (Compositae: Cynareael are troublesome weeds in North America. They are attacked by about 340 species of phytophagous insects, including 71 that are oligophagous on Cynareae. Of these Eurasian insects, 39 were extensively tested for host specificity, and 5 of them were sufficiently damf..ghg and stenophagous to warrant their release as biological control agents in North America. They include four beetles: Altica carduorum Guerin-Meneville, repeatedly released but not established; Ceutorhynchus litura (F.), established in Canada and Montana on Cirsium arvense (L.) Scop.; Rhinocyllus conicus (Froelich), widely established in the United States and Canada and beginning to reduce Carduus nutans L. populations; Trichosirocalus horridus ~Panzer), established on Carduus nutans in Virginia; and the fly Urophora stylata (F.), established on Cirsium in Canada. Potentially useful and probably host-specific fungi attacking Carduus include five species of Puccinia and two species of Uredo.