The Triservice anaesthetic apparatus is a draw-over using ambient air as the primary carrier gas. Its modules are a self-inflating bag, a vaporiser, a supplementary oxygen regulator and a ventilator; each is described. The outputs of halothane and trichloroethylene were measured with changes of temperature, continuous and intermittent gas flows and with alteration in barometric pressure. The output of oxygen from the Houtonox regulator was measured and the effect of the oxygen supplementation on the inspired oxygen concentration determined. The resistance to airflow of the apparatus was also measured and the effect of extreme cold observed. The merits, limitations and the way in which the equipment may be used are discussed. A carrying case with equipment for 10 anaesthetics is illustrated.