Spectral changes in the ne~ir iofrared absorption region of chromatophores of Chromatium vinosum, strain D, were analyzed. Spectral changes dependent in growing cultures on temperature (33~ and 39 ~ C, respectively) were compared to artificial changes which take place under the influence of the detergent Triton X-100. Like addition of Triton X-100 to chromatophores, transfer of cells from 39 ~ C to 33 ~ C leads to the reversible formation of an absorption band at 820 nm at the expense of a band at 850 nm. But in contrast to the influence of Triton X-100, chromatophores isolated from cells grown at 39~ (39~ chromatophores), contain on an identical bacteriochlorophyll basis, higher amounts of pigment absorbing at 880 nm and lower amounts of pigment absorbing at 800 nm than found in 33 ~ C chromatophores. Triton X-100 treatment does not influence the production of light induced absorbance changes characteristic of photochemical reaction centers; it does, however, change absorption spectra of a subchromatophore fraction which does not exhibit the known light dependent reaction center responses. The spectral properties of this fraction are altered with Triton X-100 in a manner comparable to whole chromatophores, i.e. translocation of the 850 nm band to 820 nm. Subchromatophore fractions isolated from 33 ~ C chromatophores, which display an absorption band at 820 nm show in the presence of menadione a light induced absorbance change at 835 nm. Subchromatophore fractions from 39 ~ C chromatophores, which display no absorbance at 820 nm show a light induced adsorbance change at 835 nm only after addition of Triton X-100. Spectral changes in growing cultures are accompanied by changes in the fluorescence emission spectra of isolated chromatophores. While 33 ~ C chromatophores exhibit a major fluorescence emission band at 929 nm plus a minor band at 890 nm 39~ chromatophores exhibit only one band at 937 nm.