Research on operant learning principles suggests that discriminative stimuli, and negative and positive reinforcement play a role in the maintenance of smoking behavior. Smoking research from a respondent learning paradigm focuses on the role of environmental stimuli that function as elicitors of physiological responses related to smoking. Basic research suggests that compensatory responses may play a role in drug tolerance and relapse. In one preliminary study assessing the role of compensatory responses to smoking stimuli (Machado, 2011), drops in carbon monoxide (CO) were observed only when smokers viewed smoking related stimuli. However, it is possible that these patterns were influenced by CO monitor sensitivity to differing exhalation durations in which exhalation duration may have been under stimulus control of the smoking stimuli. The purpose of the current study was twofold: Study 1 controlled for exhalation duration by holding exhalation duration constant using a within subject design and Study 2 precisely measured but did not control total exhalation duration in an attempt to replicate the results from Machado (2011). Results from Study 1 did not support the presence of compensatory responses in smokers; results from Study 2 did not support the presence of operantly maintained exhalation durations. Study limitations, implications and future directions are discussed.