Serial ordering errors in spontaneous speech often involve individual phoneme-like segments, but seldom larger syllabic components containing both consonants and vowels. This observation suggests that syllabic structure provides a framework for the serial ordering of individual phonemic segments, while larger subsyllabic units and entire syllables do not themselves undergo such ordering during normal production planning (Shattuck-Hufnagel 1979; Shattuck-Hufnagel and Klatt 1979). When speakers repeated syllable sequences constructed by alternating pairs of consonants in conflicting patterns (e.g., PAN FILL FUN POLL, where initial /p, f/ alternate in the pattern ABBA, final /n, l/ in ABAB), 95% of the errors involved a change in a single segment and only 5% involved a CV, VC, or CVC unit. These findings support the view that speech production planning involves the serial ordering of phoneme-like segments, and not of larger syllabic components. Further questions about the nature of position constraints on segments interacting in errors, and about the role of word stress in constraining single-segment errors, are also being explored using this method.