Data are presented for the duration of syllables in American Sign Language and for movement and hold components of those syllables. Measurements from 3072 syllables taken from four different samples of signing resulted in a grand mean of 293.7 msec. The different signing samples reflected different degrees of naturalness, and the means for each sample varied accordingly. The most natural situation, conversational signing, had a mean of 249.7 msec, comparable to the quarter of a second reported for spoken English syllables. Less natural situations, involving clicitation tasks, showed higher means (292.1 to 360.7 msec). Different syllable types varied in their duration. The presence of a final hold significantly increased the syllable duration. Statistical analysis revealed three distinct groups of syllabic types as a function of duration: short, long, and extra long. A specific test of the claim that linguistic stress significantly increases the duration of syllables was not confirmed; instead, stressed targets differed from unstressed targets in having a greater number of syllables. A related claim that the duration of movement when stressed is significantly shorter than when not stressed was also not confirmed.