Whole-body burdens of radionuclides, especially cesium-137, were determined in 703 northern Alaskan Eskimos during the summer of 1962. Correlation of these amounts with dietary information obtained from the subjects showed Cs137 body burdens were directly related to amounts of caribou or reindeer consumed. Maximum Cs137 body burdens were found in residents of Anaktuvuk Pass, where an average adult contained about 450 nc. Lowest values occurred among Eskimos who ate substantial amounts of marine mammals and fish. Natives in equilibrium with the principal source of Cs137 in their diet contained body burdens about 10 times their weekly Cs137 intake. Various factors affecting the Cs137 body burden found during the study are discussed.