The aim of this research was to verify characteristic morphological changes in the liver with regard to survival time after laser irradiation. The duration of irradiation was constant. For the purpose of irradiation we used a helium-neon laser. The value of the energy absorbed during the exposition amounted to about 2.5 J. Segments from the irradiated liver field of rats were taken directly after decapitation following different times of survival the changes were estimated in an ultrastructural microscope. Our results showed dependence of certain morphological changes (perceptible only by ultrastructural examination) on the time of survival after irradiation.