This report describes a simple analogue computer, developed for the analysis of breathing mechanics. The complete apparatus consists of 2 transducers (for pressure and flow), 6 operational amplifiers, 1 multiplier, 4 coefficient and 4 preset potentiometers, an oscilloscope, counter unit and programme board. The computation is performed in real time on continuous variables, by a null method, using the oscilloscope to display the output. The equipment is being applied to the study of airway obstruction in lung disease. As well as the usual compliance and resistance, a factor related to collapsibility of the airways has been measured. The apparatus is easy to handle, gives results quickly, and is flexible enough to be used to explore relationships between variables as well as to measure familiar quantities.