Airflow interruption in the breathing pattern of guinea pigs exposed to a high concentration (35 mg/m³) of cotton dust was examined using a chest-flow versus airway-flow two-chamber plethysmograph. Results showed that airflow interruption occurred most often during the latter phase of lung deflation. At high breathing rates the interruption and subsequent initiation of flow was associated with a deceleration - acceleration of the gas in the airways and was responsible for an oscillation superimposed on the airflow pattern. This oscillation appeared as airflow interruption during deflation and especially during lung inflation. Airflow interruption was also seen, but much less frequently, along other regions of the flow-flow and flow-volume patterns of the lung. These interruptions occurred with very little alterations in specific airway resistance and were thought to be caused by changes in respiratory muscle activity.