Electric fields as high as 10(5) V/cm cause polarization of chromatophores and reaction centre films prepared from photosynthesizing bacteria. Photosynthetic pigments, carotenoids in particular, the absorption spectra of which are changed in response to electric fields, may serve as an intrinsic indicator of the development of a polarized state. Polarization occurs due to changes in orientation and spacial position of different charge groups and particles. The field-induced polarized state can be fixed up by exposure to low temperature (-120 degrees C). While heating the system relaxes to the initial state and this can be seen as a current in an electric circuit. The effects of hydration, chemical modification or heat treatment on current indicate the involvement of macromolecule components in the formation of a polarized state, In light-adapted samples the polarization effect is markedly greater and this can indicate that conformational changes occur during the primary photoact. It is supposed that polarization might be implicated in the stabilization of separated charges and in the storage of energy.