The three‐dimensional crystallization of bacteriorhodopsin was systematically investigated and the needle‐shaped crystal form analysed. In these crystals the M‐intermediate forms 10 times faster and decays 15 times more slowly than in purple membranes. Polarized absorption spectra of the crystals were measured in the dark and light adapted states. A slight decrease in the angle between the transition moment and the membrane plane was detected during dark adaptation. The crystallization of a mutated bacteriorhodopsin, in which the aspartic acid at residue 96 was replaced by asparagine, provided crystals with a long lived M‐intermediate. This allowed polarized absorption measurements of the M‐chromophore. The change in the polarization ratio upon formation of the M‐intermediate indicates an increase in the angle between the main transition dipole and the membrane plane by 2.2 degrees +/‐ 0.5, corresponding to a 0.5 A displacement of one end of the chromophore out of the membrane plane of the bacteriorhodopsin molecule.