According to Eguchi (1934), two species of salmon (Oncorhynchus) serve as a source of human infection by a cestode indentified as Diphyllobothrium latum (Linnaeus, 1758), in Japan. The possible role of these fishes in the transmission of cestodes to man and other animals has not been investigated in North America,nor, apparently, on the Eurasian mainland. However, Ward (1930) reported unidentified Diphyllobothrium-like plerocercoids from Alaskan salmon; Simms and Shaw (1931) collected plerocercoids identified as D. cordiceps (Leidy, 1871) from Oncorhynchus kisutch (Walbaum) from lakes in Oregon; and Wardle (1932) reported plerocercoids of Diphyllobothrium spp. from O. kisutch and O. nerka (Walbaum) in western Canada. Five species of Oncorhynchus occur in the waters of Kodiak Island, and all are important as human food. Aboriginal methods of preparing fishes for human consumption are such that cestode larvae might remain viable for some time. Localization of plerocercoids in parts of the fish used for food would provide opportunity for human infection.An investigation of the ecology and taxonomy of the species of Diphyllobothrium occurring on Kodiak Island was undertaken by the writer in 1952, the results of which are reported here. Emphasis has been placed on morphological variation in Diphyllobothrium.