This study provides acoustic evidence that in the last 50 years New Zealand English (NZE) has undergone a substantial vowel shift. Two sets of data are studied: the Otago corpus, recorded in 1995, and the Mobile Unit corpus, recorded in 1948. Both corpora have male and female speakers. The corpora were labeled, accented vowels were extracted, and formant values were calculated. The results of the formant analysis from the two corpora are contrasted. We provide evidence that in NZE /i/ has centralized, /e/ and /æ/ have raised, and the diphthongs /iƏ/ and /eƏ/ have merged. We argue that /i/ changed in quality not only because of crowding in the front vowel space, but also because it would be less likely misperceived as an unaccented vowel (i.e., as Ə).