Conflicting reports in the literature on the relationship between the pigment content of chromatophores and that of the whole cells from which they have been isolated are reviewed. Chromatophores, isolated in sucrose density gradients from organisms grown at high light intensity or at very low oxygen tension in the dark, had a content of bacteriochlorophyll proportional to the pigment content of the cell. It was shown, however, by chemical analyses and by electron microscopy that these 'chromatophores' were heavily contaminated with other cellular structures. It is suggested that the inability to obtain pure material from cells grown under these environmental conditions is due to differences in their internal organization, resulting in a different pattern of fragmentation on disruption. When growth was at low to moderate light intensity, chromatophores of constant composition were isolated from cells of different pigment content.