The occurrence of epizootics of lymphosarcoma in maskinonge (Esox masquinongy) and northern pike (Esox lucius) are reported. The results of a questionnaire circulated to fisheries workers around the world in attempts to locate populations of Esox infected with the lymphosarcoma syndrome are discussed. Selected field data concerning the epizootiological nature of the syndrome is presented with particular reference to the four plausible causes of the syndrome in Esox:

• environmental (carcinogens in the environment)
• genetic
• bacterial infections (e.g. infectious granuloma type lesion)
• virus