We conducted a production experiment with 1600 potentially ambiguous utterances distinguished by word boundary location in Catalan and Spanish (e.g., Cat. mirà batalles '(s)he looked at battles' vs. mirava talles 'I/(s)he used to look at carvings'; Span. da balazos '(s)he fires shots' vs. daba lazos 'I/(s)he gave ribbons'; stressed syllables are underlined). Results revealed strong effects of within-word position on H location. Peaks tended to be timed earlier with respect to the end of the syllable when their associated syllables occurred later in the word than when they occurred earlier in the word. These results confirmed previous findings for other languages (Silverman & Pierrehumbert, 1990 for English; Arvaniti, Ladd, & Mennen, 1998 for Greek; and Ishihara, 2006 for Japanese; and Godjevac, 2000 for Serbo-Croatian) and for Spanish and Catalan (Prieto, van Santen, & Hirschberg, 1995 for Spanish; de la Mota, 2005; Simonet, 2006, Simonet & Torreira, 2005 for Catalan). A set of perception experiments suggested that tonal alignment patterns influence listeners' judgments of word boundary location both in Catalan and in Spanish. Listeners were able to employ fine allophonic details of H tonal alignment due to within-word position to identify lexical items that are ambiguous for word-boundary position. The data is consistent with the view that prosodic structure plays an essential part in determining the temporal coordination of f0 contours with segmental material. © 2010 Elsevier Ltd.