Previous research on Rere has documented an eight-vowel system /i e ɛ ɐ a u o ɔ/ with strict vowel harmony rules (Quint 2009). The present study provides anacoustic analysis of the Rere vowel system to capture the phonetic characteris-tics of vowel quality in phonological distributions and phonetic processes. Usingelicited data with instrumental suffixation and valence-changing structures (including causatives and passives), we largely confirm the previous account of vowelheight agreement in Rere. However, considerable variation in vowel height andvowel quality was also observed. To account for the exceptions, we propose thatthe mid front vowel /e/ is shifting to a higher vowel [ɪ], which better explainswords with disharmonic combinations, mismatches between root and suffix vowels in the instrumental construction, and the lack of alternation in derived verbs incausatives.