A purely segmental or suprasegmental analysis of vowel harmony in Arabic is inadequate because it leaves some questions unanswered. An approach based primarily on the metrical structure of the utterance and addressing an independent structural category, the "foot" of the word, that phonological rules may refer to, is preferred, especially when amplified by some features of the suprasegmental approach to phonological rules. It is proposed that the foot is the domain of the vowel harmony rule in the sense that, for example, a vowel /i/ will become /u/ in the vicinity of another vowel /u/ if the two vowels share the same foot, and the foot, not the stem, is specified for the feature [round]. This approach explains why certain prefixal vowels are not harmonized. The stem is seen as having a significant role in limiting the segments that may be harmonized. (MSE)