Fatty material from a Thule Eskimo site on Herschel Island, Yukon Territory, Canada was analysed by gas chromatography and thin layer chromatography. The fatty acid composition of the samples was then compared with published data for a number of marine species which could have been food sources for the Thule peoples. The samples appear to be derived from seal or whale, or a mixture of these, but what is more surprising is that the fats have changed so little over the 1000 year period of their burial.