We describe a procedure for acquiring intonational phrasing rules for text-to-speech synthesis automatically, from annotated text, and some evaluation of this procedure for English and Mexican Spanish. The procedure employs decision trees generated automatically, using Classification and Regression Tree techniques, from text corpora which have been hand-labeled with likely locations of intonational boundaries by native speakers, in conjunction with information available about the text via simple text analysis techniques. Rules generated by this method have been implemented in the English version of the Bell Laboratories Text-to-Speech System and have been developed for the Mexican Spanish version of that system. These rules currently achieve better than 95% accuracy for English and better than 94% for Spanish.