This study investigates the relationship between variation due to prosodic prominence and variation due to sound change. We compare two hypotheses: under prominence vowels move in the direction of vowel shift, and under prominence vowels are hyperarticulated, and move to positions more peripheral in the vowel space. These hypotheses make competing predictions for two vowels currently undergoing change in Chicago American English, /ε/ and /uw/. Labov  reports that in the Chicago variety, which participates in the Northern Cities vowel shift, the most recent changes have affected the vowels /ε/ and /Α/, both of which have been retracting since about 1980. In addition, as in many other contemporary varieties of English, the vowel /uw/ has been reported to be fronting. This fronting is not necessarily part of the general vowel shift. An acoustic analysis of controlled vowel productions from 20 speakers in their twenties shows that prominence effects are consistent with the hypothesis of prominence as local hyperarticulation, but do not generally support the claim that prominence and vowel shift effects are in the same direction. The findings also reveal /uw/ fronting as a change in progress, with greatly more variation in the front/back dimension than for other vowels, in all prosodic contexts. Other effects of prominence on vowel height are discussed as indicators of future vowel changes in this variety.