Hoemeke and Diehl [J. Acoust. Soc. Am. 93, 2422(A) (1993)] reported that the perceptual boundary between [+high] and [−high] English vowels occurs at an F1–F0 distance of 3–3.5 Bark and that this boundary is sharper than those for other height contrasts. This suggests that the 3- to 3.5-Bark distance, corresponding to the range of the ‘‘center of gravity’’ effect [L. Chistovich and V. Lublinskaja, Hear. Res. 1, 185–195 (1979)], affords a perceptually natural boundary. In the current study, listeners performed a 0.5-Bark step F1–F0 discrimination task on one of five series of single formant stimuli. F1 ranged from 2.5–7.0 Bark within a series, and F0 ranged from 1.0–2.0 Bark between series. Significant linear effects of both a formant/harmonic interaction (r=0.68) and F1–F0 distance (r=0.71) were found (multiple R2=0.94). However, a peak in discriminability near F1–F0=3–3.5 Bark was not observed. Thus the relatively sharp [+high]/[−high] boundary does not appear to be owing to enhanced discriminability. [Work supported by NIDCD.]