During the summer of 1976 an investigation into the nature of genetic variability in the cutthroat trout (Salmo clarki) was initiated. The results presented here are the product of only one summer's data, and will be subject to rigorus testing in the next two summers. This project has been supported in part by a New York Zoological Society Scholarship and a National Science Foundation Energy-Related Traineeship. I wish to thank Pete Hayden of Grand Teton National Park, Max Rollefson, Jon Erickson, and John Kiefling, of the Wyoming Game and Fish Commission, and John Varley and Ron Jones of the U.S. Fish and Wildlife Service for their cooperation in collection of cutthroat trout. I would also like to thank Drs. R .M. Kitchin, H. Bergman, and G. T. Baxter, of the Department of Zoology and Physiology, University of Wyoming for their help in organizaing this research project.