1 This paper is a revised and extended version of The Position of Waiilatpuan in Plateau Linguistic Prehistory, which I read at the 1965 Northeastern Anthropological Conference meetings at Vassar College, and sections of my Ph.D. dissertation, Linguistic Relations in the Southern Plateau (University of Oregon, 1965). It is based in part upon field research which was supported by funds administered by Joe E. Pierce of Portland State College from a National Science Foundation grant, GS-72, for the study of near-extinct indigenous languages of Oregon. I wish to thank William W. Elmendorf, David French, and Theodore Stern, with whom I discussed aspects of the research described in this paper. My former student at the University of Toronto, Laird Christie, assisted me in the ethnohistorical research. I owe a special note of thanks to Margaret C. Blaker, Archivist at the Office of Anthropology, U. S. National Museum. Mrs. Blaker located Cayuse and Molala manuscripts for me with dispatch and enthusiasm. Perhaps additional new Cayuse materials will be found when the J. P. Harrington Collection at the Archives is catalogued and examined. I alone am responsible for the shortcomings of this paper. 2 Horatio Hale, Ethnology and Philology, United States Exploring Expedition, during the years 1838, 1839, 1840, 1841, 1842 (Philadelphia, Lea and Blanchard, 1846). Hale gathered linguistic materials from several Sahaptin dialects, Nez Perce, and Cayuse in 1841. He had earlier colin their relationship has never been treated of the literature. Thus, a Waiilatpuan grouping, under one name or another, has been cluded in all subsequent classifications of North American indigenous languages.3 In the published account Hale said absolutely nothing about this proposed genetic relationship; he simply listed Cayuse and Molala forms under the Waiilatpu heading. When I first began my Cayuse-Molala investigations in 1964, I found that only about 10 percent of Hale's 180-odd CayuseMolala lexical sets showed inspectional resemblances, using generous standards of phonetic-orthographic similarity. This fact, along with one informant's information, led me to suspect that Hale had grouped these two languages together on the basis of extra-linguistic evidence of their putative mutual intelligibility probably given him by Marcus Whitman, the Protestant missionary who had established the Waiilatpu Mission in 1836.4 From the available Cayuse and