Disruptions of breathing in persons who stutter (PWS) have been documented since 1931 (7); they have been associated with perceptually fluent and stuttered speech and with nonspeech tasks. Yet there has been little recent investigation of respiratory control in PWS, and its contribution to the etiology of stuttering is unknown. The research proposed here is designed to increase understanding of the place of respiration within a multifactorial model of stuttering (80, 81, 83, 104). Identification of aspects of respiratory control associated with high risk for disfluency is seen as prerequisite for delineating the interaction of respiration with other variables which also play a role in the development and maintenance of stuttering. The research proposed here is designed to address three broad questions: 1) In normal speakers, what happens to known instabilities in the control of life-support breathing when speech is initiated? How do these instabilities affect stuttering speakers? 2) Does a general inability to take control of respiration characterize the motor systems of persons who stutter? 3) Is respiratory control in PWS more reactive to arousal associated with cognitive and emotional processing? For all of these questions, preliminary data implicate dynamic processes, thus, there is an emphasis on tasks that impose timing constraints, and on analyses that go beyond long-term averages to look at how respiratory control processes change over time in both normal and stuttering speakers. Among therapies in current use, the status of respiratory control ranges from major focus to nonexistent (20). Improved understanding of the role of respiration in stuttering has the potential to effect major change in the practice of therapy for this disorder, which affects approximately 1 percent of the adult population worldwide.