A series of experiments was conducted to examine the influence of contrastive stress on intonational patterns of duration and fundamental voice frequency (F0). In a preliminary study, intonational patterns in spontaneous speech were compared with the patterns in oral reading of the transcribed spontaneous material. In both circumstances, a general declination of F0 peaks throughout the course of a sentence was not regularly observed, contrary to earlier findings with oral reading of isolated sentences. Two experiments were then conducted to examine the possibility that the general absence of declination observed here might be due to the influence of sentence focus, following previous results from Swedish showing that declination was not observed consistently in isolated sentences until after the site of focus. In experiment 1, we found no evidence of this restriction on declination in the oral reading of English declaratives. Declination was observed both before and after the focused item in a sentence. Furthermore, our analyses revealed that focus (as manifested by contrastive stress) is generally accompanied by an increase in duration on the focused word and by a sharp drop in F0 following the focused item. In experiment 2, these effects were replicated and extended using longer sentences. In both experiments, the influence of focus was strictly localized to the site of focus in the case of duration, but not F0. The results for both duration and F0 indicate that the influence of focus assignment on these attributes varies systematically as a function of the focus location in the sentence. Finally, the combined elongation effects for focus and utterance-final lengthening were less than would be predicted by an additive model, suggesting the operation of an expandability constraint on segmental lengthening in speech production.