The author proposes that dissimilation, like assimilation, be considered a natural linguistic process, motivated by perceptual (psychological factors, which operates to preserve the distinctiveness of the stem-affix relationship. Defining dissimilation as the process which occurs when twosegments in the same word share the same phonetic features and one of the segments, usually the second of the pair, causes the other to either change one or more of its phonetic features or to be deleted, the author cites several examples of phonetic and morphophonemic dissimilation. In the examples presented, dissimilation is considered a perceptual universal with the function of enhancing the prominence of concatenated morphemes. (VM)