Lifetime of a laser system composed of a master oscillator and two light amplifiers emitting within a narrow spectral interval ( Dl≤0,01 nm) has been investigated experimentally. In this system the ethanol solution of the coumarine-2 dye is pumped by radiation of a Xe-Cl-laser. It is shown that lifetime of such a system exceeds the lifetime of a laser system with nonselective resonator and depends on the cell length and dye concentration in the amplifier. It was revealed in this study that there exists a stabilization of dyes by the laser emission. It is shown that it is necessary to select the laser construction in accordance with the application and to optimize the laser efficiency by varying the dye concentration.