THE complex annual plumage changes of Rock Ptarmigan (Lagopus mutus) have attracted frequent study. Two investigations are outstanding in scope and thoroughness: Salomonsen's (1939) monumental work on descriptive aspects of plumages and feather replacement and A. Watson's study (The annual cycle of Rock Ptarmigan. Ph.D. thesis, University of Aberdeen, 1956) of free-ranging ptarmigan in arctic Canada and Scotland. Careful examination of hundreds of museum skins enabled Salomonsen to postulate a number of relationships between molt and breeding cycles; many of these ideas were confirmed by Watson's extensive field research. I was able to get information on summer plumage changes of live-trapped Rock Ptarmigan while studying population changes among these birds on breeding grounds in central Alaska. These observations, made in an area from which Salomonsen had little material and where Watson had few field observations, extend and clarify some aspects of molt discussed by those authors. This is especially true regarding year-to-year changes in molting schedules and the rates of molt of remiges. I am grateful to the Alaska Department of Fish and Game for the opportunity to gather and analyze these data in connection with Federal Aid in Wildlife Restoration Projects W-6-R and W-13-R. My wife, Judith S. Weeden, Alan Courtright of the Alaska Department of Fish and Game, and George C. West, Laboratory of Zoophysiology, University of Alaska, reviewed and ably criticized the manuscript.