The dynamics of voluntary cough were studied in healthy supine subjects during four successive infusions of d-tubocurarine (dTc) (0.05 mg/kg) to assess the effects of progressive expiratory muscle weakness on cough performance. Curarization produced a progressive decline in maximal static expiratory muscle strength (PEmax) measured at the mouth and in pleural pressures (Ppl) generated during coughing. Expiratory flow rates during coughing did not decrease except during the initial cough from total lung capacity with the last dTc dose (18% below control). This was associated with a decrease in end-inspiratory volume prior to coughing and with a marked decrease in Ppl to 30% of control. Although the decrease in flow rates was minimal compared with Ppl, flow patterns suggest that dynamic airway compression was reduced during these coughs. We conclude that the principal effect of the expiratory muscle weakness in curarized subjects is to reduce the cough-induced dynamic compression and linear velocity of airflow though the major intrathoracic airways.