Some of the problems inherent in a word-based hypothesis asserting that the word/stem is taken as the minimal sign not only for syntax but also for morphology are examined in an analysis of a polysynthetic language, Koyukon, an Athabaskan language of Alaska. Data from the Central dialect is considered in the analysis. A brief sketch of the verbal system of Koyukon is presented, followed by consideration of the following specifics of the word-based hypothesis: the Binary Branching Hypothesis and the No Phrase Constraint. The remainder of the paper outlines some of the complications involved in a computational analysis of Koyukon following a theory of word-based morphology. (CB)