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The breeding and feeding of Kerguelen Terns (Sterna virgata) and Antarctic Terns (S. vittata) were studied at the Kerguelen Islands in January-February 1985. The laying period was estimated to have ended during the third week of December for Kerguelen Terns and started during the last week of December for Antarctic Terns. Kerguelen Terns used a wide variety of feeding techniques and fed in marine, freshwater and terrestrial habitats. Marine crustaceans, fish and terrestrial invertebrates were the main prey. Antarctic Terns fed only in marine habitats, where crustaceans were the main prey. Even when feeding close together, the terns were seldom aggressive. Contrary to previous reports, Kerguelen Terns fed fish to chicks and fledglings despite the presence of Antarctic Terns. Frequent strong winds prevail at the subantarctic islands, and so wind speed is probably the most important factor affecting the ecology of Kerguelen and Antarctic terns.