This paper reports an empirical study designed to explore whether concurrent verbal reporting has a reactive effect on the process of second language writing. Ninety-five Chinese EFL learners were randomly assigned to an argumentative writing task under three conditions: metacognitive thinking aloud (MTA), nonmetacognitive thinking aloud (NMTA), and no thinking aloud (NTA), after they completed a similar baseline writing task. Their essays were analyzed in terms of linguistic fluency, complexity, accuracy, and overall quality to examine if there were any significant between-group differences that could be taken as evidence of reactivity. After controlling for baseline differences, analyses revealed no traces of reactivity left on a majority of measures except that: (a) the two think-aloud conditions significantly increased dysfluencies in participants’ essays; (b) they also tended to reduce syntactic variety of the essays; and (c) MTA significantly prolonged time on task and retarded the speed of written production. These negative effects are interpreted in light of Kellogg's (1996) cognitive model of writing as suggesting no serious interference with L2 writing processes and are taken as cautions for, rather than counterevidence against, the use of the think-aloud method to obtain L2 writing process data.