Dry orderly oriented purple membrane from Halobacterium halobium was obtained by a new technique of preparation. This oriented purple membrane film was very stable, nearly permanently, and showed long term reproducibility with respect to its photochemical behavior. In addition, we have investigated the photooptical properties in terms of the M$_{412}$ intermediate of the bacteriorhodopsin photocycle with respect to the humidity of the film. The relative optical density, i.e. its apparent concentration of the M$_{412}$ intermediate was decreased with the humidity increase as a function of the intensity of the exciting flash within our experimental range. It is suggested that the bound water molecules play an important role in the structure of the bacteriorhodopsin.