Often when vowel loudness is measured, only SPL, duration, fundamental frequency, and formant frequencies are considered as causes of loudness. In the present study, differences in loudness were measured which apparently are a function of the mode of laryngeal vibration. Stimuli were constructed by having speakers produce a series of vowels at a single fundamental frequency and at several sound pressure levels (SPLs). The sustained vowel sounds were then electronically equalized for SPL and presented to subjects as pairs of isolated vowels. Differences in loudness were reported by subjects when asked to make paired comparisons. Vowels with equal duration, SPL, formant frequencies, and fundamental frequency were judged to be different in loudness as a function of the phonation quality associated with the vowels' position in the voice range of the speakers.