In English and Dutch, pitch accents occur only on lexically prominent syllables. Such syllables are not always accented in longer utterances, however, and traditional descriptions differentiated ``stress'' proper as a local increase in loudness, although the intonational event is the most salient cue to prominence, far outweighing any differences in overall rms amplitude. Recent work by Sluijter and colleagues [J. Acoust. Soc. Am. 101, 503--513 (1997)] indicates that stressed syllables in Dutch are associated with differentially increased energy at frequencies well above the fundamental, and that these spectral tilt differences are a robust cue to relative syllable prominence --- whether or not the word is in focal prominence. Because accents are not necessarily associated with focused words, however, their experiments do not tell us whether spectral tilt differentiates lexically stressed from unstressed syllables in the absence of an associated intonational prominence. The current study examines five acoustic measures, including spectral tilt and open quotient, for accented, unaccented but stressed, and unstressed syllables in a corpus of utterances produced by four speakers of American English. Results confirm that spectral tilt is affected by accent independent of F0 increase, and that it is affected (to a lesser extent) by stress in the absence of accent.