Four experiments investigate the scope of grammatical planning during spoken sentence production in Japanese and English. Experiment 1 shows that sentence latencies vary with length of sentence-initial subject phrase. Exploiting the head-final property of Japanese, Experiments 2 and 3 extend this result by showing that in a 2-phrase subject phrase, sentence latency varies with the length of the sentence-initial phrase rather than that of the whole subject phrase or its head phrase. Experiment 4 confirms this finding in English. The authors' interpretation suggests that these effects derive from grammatical encoding processes. Planning scope varies according to the relation between the 2 phrases composing the subject phrase. A thematically defined functional phrase is suggested as defining this scope.