The quantum efficiency and the molar-absorption coefficients of different phenothiazine dyes are obtained by means of fitting the experimental data of transmittance as a function of time. An analytical expression for the intensity transmitted in a photopolymerizable holographic material is obtained, and good agreement between theory and experience is also achieved. The analysis of these parameters is of fundamental quantities in the photochemical characterization of holographic recording materials. ; This study was supported by the Direcció General d'Ensenyaments Universitaris i Investigació de la Generalitat Valenciana, Spain (Project GV-C-CN-06-064-96).