A new species to be added to the list of birds known to occur in Utah is the Bay-breasted Warbler (Dendroica castanea). Two warblers were seen by the authors very late in the afternoon of 25 May 1974 foraging in a mixed growth of cottonwoods and squawbush along the floodplains of the White River at an elevation of 5200 feet about five miles east of Bonanza, Uintah County, northeastern Utah. Realizing that they were different, but not knowing for certain what kind of warbler was represented, the junior author collected one. It proved to be a fat male with testes measuring 6 x 4 mm. It is now number 22249, University of Utah collection. The identity of the second warbler could not be ascertained.