This paper discusses processing units in speech production among bilinguals. First, naturally occurring intrasentential code-switching (switching languages within a sentence) was examined to show that bilinguals switch at syntactically definable constituent boundaries. Next, a code-switching elicitation experiment on Japanese/English bilinguals was conducted in which subjects were asked to speak about topics given and asked to switch to another language upon hearing randomly generated tones at 8–12 second intervals. The results suggest that bilinguals switch constituent-by-constituent and that this switching pattern is similar to monolinguals ' processing unit.