Abstract
(1) The occurrence of outbreaks of Diphyllobothrium in trout and related forms is reviewed.(2) A survey of the occurrence of Diphyllobothrium in Great Britain has been made. Plerocercoids of Diphyllobothrium have been found in approximately half of the areas from which trout have been examined. Three species of Diphyllobothrium at least have been found to infect trout and related species of freshwater fish in this country.