The intense infra-red rays of the CO2 laser effect instant evaporization and carbonization of superficial tissue layers. Simultaneously, small blood vessels in the immediate vicinity of the impact area are occluded, which results in a circumscribed ischaemic operating field. On the other hand, small lymphatic vessels are not sealed. The lymphatic drainage of an area can be blocked mechanically only by a relatively large wall of carbonized tissue. This is why laser surgery does not necessarily prevent propagation of suspended material in the lymphatics, e. g. tumour cells.