The purpose of this investigation was to determine whether function words are lengthened in certain phrase positions in mother-to-child speech. Twenty-two mother-child dyads served as subjects. All children (ages 1:5 to 2:2) had a mean length of utterance between 1.0 and 1.5 morphemes. Each mother was asked to read five experimental stories aloud to her child and to an adult. The durations of seven function-word vowels in these stories were examined. Each word appeared in three phrase positions (phrase-initial, phrase-medial, and two types of phrase-final). Function-word vowels in initial and medial positions did not differ significantly in adult-directed and child-directed speech. In contrast, function-word vowels in final position were significantly longer in mothers' speech to their children.