For investigation of influence of reactive oxygen species on biological systems the peculiarities of light scattering and fluorescence spectra of aqueous solutions in the presence of photoactive additions of acetone (5 x 10(-4) - 30) and anionic probe ANS (5 microg/l-10 mg/l) have been considered. In water and diluted aqueous acetone and ANS solutions, long-term spontaneous variations in parameters of light scattering and fluorescence spectra have been detected. It has been found that the spectral parameters and the character of ANS influence changed drastically at acetone concentrations of approximately 0.1%, approximately (0.2-0.3)%, and approximately 0.8%. The results can be explained by rearrangement of solvent structure in the surrounding of admixture molecules, photochemical processes with the participation of acetone and reactive oxygen species, as well secondary reactions with their involvement in gas-vapor and acetone bubbles.