Singers are required to sing with a high degree of precision of fundamental frequency (F₀). Does this mean that they have learned to compensate for the change of pitch that has been described in speech during production of different vowels? Experienced choir singers sang sustained tones with a change of vowel in mid-tone. The fundamental frequency was measured, and the resulting F₀ contours were evaluated with respect to F₀ effects coincident with the vowel changes. The tasks were performed both with normal auditory feedback and with the auditory feedback masked by noise in headphones. The vowels/i/ and/y/were found to be associated with higher F₀ than other vowels. The irregularities in the F₀ curves were somewhat larger in the absence of auditory feedback. This is consistent with findings during speech production. The instability in F₀, measured as the standard deviation over each tone, was also larger in the absence of feedback.