In 1973, amphibole asbestos fibers were discovered in the municipal water supply of Duluth, Minnesota. The entire city population of approximately 100,000 was exposed during the late 1950s through 1976 at levels of 1-65 million fibers per liter of water. Because of previous epidemiologic studies which linked mesothelioma, lung, and gastrointestinal cancers to occupational exposure to asbestos, surveillance of cancer incidence in residents of Duluth was initiated to determine the health effect from ingestion of asbestos. The methodology of the Third National Cancer Survey (TNCS) and SEER Program was used. Duluth 1969-1971 rates were compared with TNCS rates for the cities of Minneapolis and St. Paul during 1969-1971; Duluth rates during 1979-1980 are compared with Duluth 1969-1971 and with Iowa SEER; and a table of the occurrence of malignant mesothelioma is presented. Statistically significant excesses are observed in several primary sites in Duluth residents.