The effect of syntactic complexity on fluent and hesitation pause durations was investigated. The stimuli consisted of five recorded sentences within which the words lost and contact were manipulated so that their syntactic relation to each other varied in complexity from sentence to sentence. Twelve subjects, working individually, mechanically adjusted the silent interval duration between the words lost and contact within each sentence in order to locate (1) the pause detection threshold, (2) optimal fluent pause duration, and (3) minimal hesitation pause duration. Silent interval duration did not differ significantly from one level of syntactic complexity to the next for either pause detection threshold or fluent pause. Hesitation pause duration, however, did differ significantly as a function of syntactic structure, in that hesitation pauses perceived within a subordinate clause boundary were significantly longer in duration than were those occurring in other types of syntactic boundaries. Further, subjects were consistent in their perceptual judgments of speech pauses from one time to the next. Individual subjects, however, showed a considerable degree of variability.