Oral resistance to respiratory airflow was measured in 5 healthy adult subjects with nasal airways occluded. Measurements were made by means of a minimally invasive plethysmographic computer-aided technique that avoided interference from a face mask or an artificial oral airway. Oral resistance ws found to be similar to that of the normal nasal airway in subjects at rest. As with nasal resistance, oral resistance decreased with increasing exercise. Four different oral airways that are used in pulmonary function testing reduced oral respiratory airflow resistance from a mean of 1.7 cm H2O/L/s to 0.2, 0.3, 0.3, and 0.5 cm H2O/L/s, respectively.