Reaction centers (RCs) of purple bacteria are uniquely suited objects to study the mechanisms of the photosynthetic conversion of light energy into chemical energy. A recently introduced method of higher order derivative spectroscopy [I.K. Mikhailyuk, H. Lokstein, A.P. Razjivin, A method of spectral subband decomposition by simultaneous fitting the initial spectrum and a set of its derivatives, J. Biochem. Biophys. Methods 63 (2005) 10–23] was used to analyze the NIR absorption spectra of RC preparations from Rhodobacter ( R.) sphaeroides strain 2R and Blastochloris ( B.) viridis strain KH, containing bacteriochlorophyll (BChl) a and b, respectively. Q y bands of individual RC porphyrin components (BChls and bacteriopheophytins, BPheo) were identified. The results indicate that the upper exciton level P y+ of the photo-active BChl dimer in RCs of R. sphaeroides has an absorption maximum of 810 nm. The blue shift of a complex integral band at approximately 800 nm upon oxidation of the RC is caused primarily by bleaching of P y+, rather than by an electrochromic shift of the absorption band(s) of the monomeric BChls. Likewise, the disappearance of a band peaking at 842 nm upon oxidation of RCs from B. viridis indicates that this band has to be assigned to P y+. A blue shift of an absorption band at approximately 830 nm upon oxidation of RCs of B. viridis is also essentially caused by the disappearance of P y+, rather than by an electrochromic shift of the absorption bands of monomeric BChls. Absorption maxima of the monomeric BChls, B B and B A are at 802 and 797 nm, respectively, in RCs of R. sphaeroides at room temperature. BPheo co-factors H B and H A peak at 748 and 758 nm, respectively, at room temperature. For B. viridis RCs the spectral positions of H B and H A were found to be 796 and 816 nm, respectively, at room temperature.