This paper describes the technique of measuring work of breathing, presented at the 13th International Symposium on Computers in Clinical Medicine and Anaesthesiology, Rotterdam, June 1992. Measuring work of breathing has clinical uses in the Intensive Care Unit. Oxygen consumption does not truly reflect work of breathing. Mechanical work of breathing can be measured by recording continuous pressure and flow and integrating the resultant power. This method is facilitated at the bedside with the use of a PC computer and a spreadsheet program. It is further simplified by software to measure the area under the inspiratory pressure: volume loop.