To evaluate the effects of photobiomodulation, we used laser devices with wavelengths of 662 nm (ALOD-01; Alcom Medica, Russia) and 808 nm (ALPH-01 Diolan; NPP VOLO, Russia) and an energy density of 1-15 J/cm2. The experiments were carried out on Paramecium caudatum (Alveolata: Ciliophora: Oligohymenophora: Peniculia). The results were evaluated before and 5, 10, 30, 60 min and 24 h after irradiation. 5 min after exposure to red light (662 nm), motor activity of infusoria increased vs. control and then decreased within 60 minutes. After 24 h of irradiation at an energy density of 15 J/cm2, the speed of infusoria was 52 % of the initial (73 % in the control) (p < 0.05). Immediately after exposure to infrared radiation (808 nm) and during the first hour, motor activity tended to decrease. 24 h later, the speed decrement was significantly less than in the control. The data obtained indicate that changes in the functional state of P. caudatum arise immediately after irradiation and persist for a long time, leading either to an increased (808 nm) or a decreased (662 nm) resistance at the same values of a radiation energy density. The peculiarities of the P. caudatum response to red vs. infrared irradiation appear to be due to the differences between primary photoacceptors and appropriate signaling pathways which come into action immediately upon their excitation.