Аннотация:A theoretical investigation is made of thermochemical bistability of a medium in which reversible chemical reactions take place under the influence of laser heating. It is shown that if a system is closed in respect of mass exchange, then a hysteresis of the temperature, absorbed laser radiation power, and other properties may be observed. When an allowance is made for the temperature dependence of the absorption coefficient of such a system it is found that the system can exhibit delayed, self-oscillatory, and triggered behavior in a laser radiation field. New types of critical phenomena in such systems are predicted.