The role of the cricothyroid muscle (CT) in respiration is unclear. To examine the respiratory-related electrical activity of the CT, we measured its electromyogram (EMG) and compared it with that of the alae nasi (AN) in eight healthy subjects. During quiet breathing the CT EMG phasing was inspiratory in seven subjects. This pattern was similar to the AN with respect to phasing and shape of the integrated EMG. The onset of phasic CT and AN activity related to inspiration preceded flow by 173 +/- 39 and 570 +/- 76 (SE) ms, respectively (P less than 0.01). We measured the duration from onset of phasic activity to peak of the EMG (TA) and the total cycle duration (TT). TA/TT of the CT was 0.29 +/- 0.02, similar to that of the AN (0.28 +/- 0.03). Inspiratory resistive loading, panting, and voluntary hyperventilation increased CT activity above the peak level seen during tidal breathing. Voluntary glottic closure increased CT activity to a level above tonic but below peak tidal activity. The findings suggest that the phasic electrical activity of the CT simulates predominantly that of an upper airway dilator.