The radiological surveillance program of the Department of National Health and Welfare is conducted for the purpose of determining levels of environmental radioactivity in Canada and assessing the resulting population exposures. Following major changes to the CAMECO Port Hope operations to reduce uranium emissions, a study was initiated to measure uranium levels in air in the community. Studies continued on lung cancer and domestic exposure to radon, and current levels of cesium-137 in caribou, a major source of food in northern communities. The movement of tritium on the Ottawa and St. Lawrence rivers was studied following an accidental release into the Ottawa River. Monitoring continued of fallout contamination from Chernobyl in imported foods. All measurements recorded during 1988 were below the limits recommended by the International Commission on Radiological Protection. (14 refs., 14 figs., 15 tabs.).