The CO2 laser emits an infra red beam with a wavelength of 10,6 mu. Focussing this beam gives a tremendous energy density. The strong absorption of this wavelength allows tissue evaporation at the focal point of the beam. The first surgical application is the use of this laser as a light knife. Satisfying haemostasis can be obtained. Vessels with an internal diameter up to 0,5 mm being sealed, haemostatic cutting is possible. Even cortical bone can easily be cut with this instrument. The ability to vaporize tissues can be used for tumor destruction. Special attachments for endoscopic surgery are available. Experimental work in the rectum and on vocal cords has been done in our laboratory. The important problem in laser surgery is the necrosis on the edges. Investigations about the viability of the margins, showed that the width of the necrosis is in linear relationship with the rate of the exposure time. For an exposure of 1/10th of a second this width was about 130 mu, for an exposure of 6 seconds about 600 mu. After one year of experimental work with the CO2 laser we are convinced that this instrument might prove to be a reliable tool in surgery.