An electrical analogue of the human lung is described. The purpose of this communication is to show the advantages to be gained by the use of a simple nonsophisticated analogue in the elucidation of problems in lung mechanics. An attempt has been made to use the analogue to predict the optimum ventilatory pattern for patients with respiratory disease who may require intermittent positive pressure ventilation. The results of two simple experiments on five analogue patients are discussed. It is possible, given the appropriate data, to arrive at these results by calculation. This, however, involves the solution of a second-order non-linear differential equation. Intuitive solution by ad hoc means is often wildly wrong and, when non-linearity is considerable, recourse must be made to digital or analogue computers. The analogue can also be used to demonstrate some of the effects of intermittent positive pressure ventilation to trainee anaesthetists.