The effects of a CO2 laser on lymphatics and small blood vessels were studied by electron microscopy. Laser incisions were made on white rats at different sites of the skin and of the mucous membranes. Electron microscopically, three zones of the lased tissue were observed: the first superficial layer consisted of a carbonized skeletal rest; the second layer was an area of coagulative necrosis; the third and deepest layer was characterized by edema of varying degrees. Small blood vessels were completely filled with erythrocyte fragments leading to an apparent occlusion of the vessels. On the other hand, lymphatic vessels of comparable size seemed to be less damaged and their lumina appeared to be open and not occluded. Our results indicate that in tumor surgery with the laser scalpel, the propagation of cellular material, e.g. tumor cells, cannot be excluded with certainty.