Analysis of a dialect's phonological change over time compares the vowel systems of individual speakers in 1971 and 1984. Subjects were four speakers of Montreal French. Two were born between 1910 and 1920, and two between 1944 and 1950. One individual in each pair was upper middle class and one was not, and no change of social status occurred during the period of the study. The linguistic features examined in the speech of the individuals include chain shifting and lexical diffusion. The three following conclusions are drawn: (1) lengthened vowels do not follow the pattern of chain shifting proposed in previous research; (2) the hypothesis that lexical diffusion is necessarily ultimately resolved is not supported; and (3) fine acoustic phonetic analysis demonstrates that phonological changes can continue after adolescence for native speakers of a dialect. The change is not conscious, and is more significant for speakers whose phonology was originally more conservative. (MSE)