Background: The technical component of Motivational Interviewing (MI) posits that client language mediates the relationship between counselor techniques and subsequent client behavioral outcomes. The purpose of this study was to examine this hypothesized technical component of MI in smoking cessation treatment in more depth. Method: Secondary analysis of 106 first treatment sessions, derived from the Swedish National Tobacco Quitline, and previously rated using the Motivational Interviewing Sequential Code for Observing Process Exchanges (MI SCOPE) Coders Manual and the Motivational Interviewing Treatment Integrity code (MITI) Manual, version 3.1. The outcome measure was self-reported 6-month continuous abstinence at 12-month follow-up. Results: Sequential analyses indicated that clients were significantly more likely than expected by chance to argue for change (change talk) following MI-consistent behaviors and questions and reflections favoring change. Conversely, clients were more likely to argue against change (sustain talk) following questions and reflections favoring status-quo. Parallel mediation analysis revealed that a counselor technique (reflections of client sustain talk) had an indirect effect on smoking outcome at follow-up through client language mediators. Conclusions: The study makes a significant contribution to our understanding of how MI works in smoking cessation treatment and adds further empirical support for the hypothesized technical component in MI. The results emphasize the importance of counselors avoiding unintentional reinforcement of sustain talk and underline the need for a greater emphasis on the direction of questions and reflections in MI trainings and fidelity measures. (C) 2017 Elsevier Inc. All rights reserved.