Absorption and fluorescence emission spectra of Rhodopseudomonas capsulata, strains 37b4 (wild type), A1a+ (blue-green mutant strain), Y5 (phototroph negative, having only B-800--850 bacteriochlorophyll-carotenoid-protein complex) at 4 K, 77 K and 300 K were measured. The fluorescence emission at 890 nm of the B-870 bacteriochlorophyll band dominates the emission of other spectral forms of the strains 37b4 and A1a+, while in strain Y5 a fluorescence emission band at 865 nm of the B-850 bacteriochlorophyll dominates. Very little fluorescence was observed at 805 nm. A linear relation between relative fluorescence intensity and the exciting light intensity was observed. The integrated fluorescence yield increased as the temperature was lowered from 300 K to 4 K. The results are discussed in the light of the arrangement of pigment molecules in the membrane and the process of energy migration within the photosynthetic apparatus.