Use of a new opto-elcctronic device showed that the stressed vowels produced by a native speaker of English could be clearly differentiated according to tongue position. The distance of the tongue from four sensors located along the hard palate was measured in multiple tokens of vowels in a /b_b/ context. There was little token-to-token variability (standard deviations of less than 1.0 mm). With the exception of a reversal between the onglide of/e1/ and /∊/, the height of the tongue differed according to phonological height as expected. The tongue was lower in back vowels than corresponding front vowels, suggesting a biomechanical linkage between tongue height and frontness-backness. Schwa differed from all other vowels, from the “average” tongue configuration seen in stressed vowels, and from the “neutral” configuration in pauses. The talker, a Southerner, diphthongized /I/ and /∊/, but showed relatively little tongue movement in /aU/(compared to that in /aI/ and /OI/). Relatively little tongue movement was also seen in the /aU/ spoken by a second talker, who showed a significantly greater change in upper lip position in producing /aU/ than in /aI/ or /oI/. This finding suggests that lip rounding and tongue movement may “trade off” as articulatory means for producing the rapid spectral change in diphthongs. © 1986, SAGE Publications. All rights reserved.