BACKGROUND Exposure to remifentanil increases the incidence of pulmonary aspiration in healthy volunteers. This effect may be explained by impairment of airway defence mechanisms and/or altered swallowing function. Pressure-flow analysis is a technique that allows objective assessment of swallowing based on pressure-impedance patterns recorded during bolus swallowing. OBJECTIVES The aim of this study was to use pressure-flow analysis to quantify the effect of remifentanil on healthy pharyngeal swallowing and to compare these effects with morphine. DESIGN A double-blind, randomised, cross-over study. SETTING A tertiary care teaching hospital. VOLUNTEERS Eleven young volunteers (mean age, 23 years) and seven older volunteers (mean age, 73 years). INTERVENTIONS Volunteers were studied twice and received either a target-controlled remifentanil infusion (target concentrations: young, 3ngml -1; old, 2ngml -1) or a bolus injection of morphine (dose: young, 0.1mgkg -1; old, 0.07mgkg -1). Pharyngeal pressure and impedance were recorded with an indwelling catheter while swallowing 10 boluses of liquid during each measuring phase. Variables defining swallowing function were calculated and compared to determine drug effects. MAIN OUTCOME MEASURES Pharyngeal pressure-flow variables following remifentanil exposure. RESULTS Changes produced by remifentanil in the measured variables were consistent with greater dysfunction of swallowing. Both the strength of the pharyngeal contractions and pharyngeal bolus propulsion were reduced, whereas flow resistance was increased. The swallow risk index, a global index of swallowing dysfunction, increased overall. At the experimental doses tested, morphine produced similar, but less extensive effects on swallowing. CONCLUSION Remifentanil induced dysfunction of the pharyngeal swallowing mechanism. This may contribute to an increased risk of aspiration.