Abstract The purpose of the present study was to investigate the stability of total phonational frequency range, and the stability of the elements from which it is calculated—lowest fundamental frequency and highest fundamental frequency—both within a single day and over a prolonged period. Twenty adult subjects were instructed to produce vowel vocalizations at the extremes of their frequency ranges. Lowest and highest frequencies were converted to semitones, and total range in semitones was calculated. Data were collected three times per day for two days 1–2 months apart. Results revealed that for the average subject, all measures varied by at least several semitones. Further research is needed in order to determine the sources of this intrasubject variability before these measures can be applied to clinical populations.