First of all, we recall the various mechanisms of interaction between laser radiation and biological systems. Then, the factors of the hazards to the eye are analysed: physical factors in connection with the emission (wave lenght, point or extended source, irradiance on radiant exposure, pulse shape and pulse repetition frequency), factors in connection with the physiological state of the eye (pupil size, dccomodation, look orientation, eyelid blink reflex, optical viewing instruments). The skin hazards are studied in function of emission parameters (wave lenght, irradiance or radiant exposure time, pulse shape and pulse repetition frequency) and local vascularisation. From these data, the Maximum Permissible Exposure (MPE) is defined. The various values of MPE edited by the T.C. 76 of the I.E.C. are commented.