Biological effects of laser radiation (LR) are determined by the absorption properties of the irradiated tissues and physiological characteristics of radiation. The high intensities of the effect are accompanied by melting, evaporation, substance ionization, formation of shock and acoustic waves. Under the action of the low-intensity LR there prevail photochemical, photobiological and thermal processes. The action of LR of one or another wave length is determined by the initial stages of its interaction with biological substrate. The biostimulating action of LR is widely used in clinical medicine. On the contrary, the effects that give rise to morphofunctional lesions of biological tissues determine the necessity of elaborating preventive measures ensuring protection of man from LR. It is generally accepted that thresholds of the damaging action on the retina and skin may be used as the main criterion for maximum allowable level (MAL) basing. In addition to the changes observable in the directly irradiated tissues, many authors point to a possibility of functional disturbances on the part of certain organs and systems of the body, followed by the formation of asthenic and vegetovascular syndromes. The experimental and clinical data confirm that the body may develop common nonspecific changes which, together with the local damaging effects, can be regarded as criteria for an adverse action of LR and, therefore, taken into account in MAL derivation.