We have established earlier that 835-nm infrared laser irradiation results in a dose-dependent growth inhibition of human mesenchymal stem and melanoma cells and is able to induce cell death. In this work we have demonstrated that hydrogen sulfide donor NaHS is able to protect both cell types from the negative action of laser irradiation and the magnitude of protection depends on NaHS concentration. The mechanism of cell protection by NaHS is primarily attributable to its effects on intracellular processes occurring after irradiation, since the protective effect does not depend on whether NaHS is added before or after irradiation. Moreover, NaHS is able to exert its protective effect even when added 6 hours post irradiation.