Meaningful Bolivian Quechua utterances, each containing one of three classes of voiceless stops (unaspirated, aspirated, and glottalized), were spoken by a phonetician who attempted to imitate the productions of the same utterances by a native Bolivian. Electromyographic recordings from the sternohyoid muscle (SH) reveal that three relatively independent factors influence the height of peaks in SH activity: vowel stress, vowel identity, and stop manner category. A peak in SH activity is associated with voice onset for the vowel following release of oral stop closure. (Consequently, for a vowel following an unaspirated stop, the peak is nearly coincident with oral release; the peak is delayed relative to release of aspirated and glottalized stops.) Ceteris paribus, SH activity peaks higher for stressed than for unstressed vowels. For equally stressed vowels, the peak at voice onset is higher for /u/ than for /i/ than for /a/. Given the constant vocalic environment /ay_'u/, the SH activity peak at voice onset following the stop of interest is highest following aspirated stops, next highest following glottalized stops, and lowest following unaspirated stops. [Work supported in part by NINCDS and NIDR.]