For the past eight years, this laboratory has been conducting GC/MS exploration studies of organic chemical residues in fishes from major U.S. watersheds. One of the frequently occurring classes of chemicals isolated by multi-class analytical techniques, such as gel permeation chromatography, is n-alkanes. Odd-numbered alkanes with 13-19 carbon atoms are often the most abundant, and are predominanted by n-heptadecane. The presence of these compounds seem to indicate normal biosynthesis in aquatic ecosystems (MCINNES et al. 1980), whereas their absence or the presence of other hydrocarbon mixtures which obscure the natural hydrocarbons may be indicative of an adverse impact on the ecosystem (VEITH et al. 1979). This study presents quantitative data for background levels of these compounds in fishes from selected eastern Montana watersheds. Sampling sites were chosen to represent watersheds having coal extraction and conversion activities and those that do not. In comparison, data is also presented for Great Lakes fish.