This article reports on a study aimed at testing the hypothesis that, because of strategic and temporal variables, composing rate and text quantity may not be valid measures of writing fluency. A second objective was to validate the mean length of writers' translating episodes as a process-based indicator that mirrors their fluent written production rather than the factors that may be related to it. The translating episode is defined as any chunk that has been written down and terminated by a pause of three or more seconds or by any composing behaviour. Data for the study were drawn from the think-aloud protocols generated by 30 Egyptian university students writing in their second language (L2) and from their retrospective interviews. To examine the validity of the three indicators, the participants' composing rates, text quantity, and translating episodes were related to their scores on an argumentative writing task and on three linguistic tests. The results of the quantitative and qualitative analyses confirm the hypothesis tested and provide evidence for the validity of this newly developed indicator of writing fluency. Implications and suggestions for further research are presented.