We present experimental results on optical properties of the rat skin controlled by administration of osmotically active chemical, such as glycerol. In vivo reflectance and in vitro reflectance and transmittance spectra of the rat skin were measured. Results of experimental study of influence of glycerol on reflectance spectra of the rat skin are presented. The significant increase of transmittance and decrease of reflectance of the rat skin under action of osmotical agent are demonstrated. Basing on mathematical modeling the optical parameters of the rat skin are determined.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.