Abstract: A method of measuring lung function in a subject includes connecting a pneumotach in series with the subject's airway and taking pressure readings upstream and downstream of a fixed resistance element in the pneumotach. Second pressure readings are taken with a second resistance element in place, and the sets of readings are processed to calculate characteristic flow curves for the subject's airway. First and second time constants are calculated from the flow curves, and are used to calculate values of lung compliance and airway resistance. The invention extends to a pneumotach device with a fixed first resistance element and a removable second resistance element. The invention also extends to apparatus for monitoring lung function including the pneumotach device, together with a pair of pressure sensors and a processor circuit for carrying out the necessary calculations of the time constants, and the lung compliance and airway resistance values.