The application of dielectric spectroscopy (DS) to the study of bacteriorhodopsin (bR)-containing purple membrane films is presented in this paper. Two types of bR membrane films, oriented and nonoriented, were investigated in a wide frequency range (10(-2) - 3 x 10(9) Hz) and temperature interval (5 -70 degreesC). Four relaxation processes were observed in this frequency range and ascribed to different mechanisms, related to the structural units of the system. A large nonreversibility of the dielectric response as a result of heating and cooling has been observed in the slow processes implicating a change in the structure of the membrane stacking depending on the history of cooling and heating of the sample. Significant changes as large as 3 orders of magnitude in the mobility have been observed in this time scale. Comparison of the oriented and nonoriented bR membrane films was performed, and it was found that the oriented purple membrane has a unique liquid crystal-like ferroelectric behavior.