The isotopic dietary method has been applied to samples of some 65 Thule Culture individuals from existing archaeological collections of Greenlandic human skeletal material. The aim was to use the Greenlandic Thule Culture as a test of the isotopic method, in that we know they were heavily dependent on marine resources, and should thus provide a direct measure of the isotopic values for humans consuming almost entirely marine protein. The sites from which the material was originally obtained encompass almost the entire periphery of Greenland. Isotopic data from a study of animals of Greenland was used as the basis for analysis. As expected, the results indicate that these people were almost entirely dependent on the marine biosphere for their protein. An exception is those from Northeast Greenland, whose isotopic signatures show evidence for consumption of terrestrial protein as well. Not expected were the observed differences at the regional and local levels.