Oriented films of purple membrane patches were assembled on solid supports by the biotin/streptavidin molecular recognition technique. The degree of biotin labeling was 0.58/bacteriorhodopsin. According to the kinetics of absorption change after flash illumination, the photochemical activity of the purple membrane was hardly affected by the biotinylation. The three steps of the oriented assembly were visualized by electron microscopy. According to surface plasmon resonance, about 0.46 ng/mm(2) of streptavidin and 1.16 ng/mm(2) of biotinylated purple membrane were in the assembled films. The amount of the nonspecifically adsorbed purple membrane, without label, was 0.44 ng/mm(2). To test the properties of this oriented purple membrane film, a similar assembly procedure was carried out with the bilayer lipid membrane system. The photoelectric voltage peak of the oriented purple membrane was 157.2 mV, whereas that of nonspecific adsorbed purple membrane was 7.8 mV. The degree of orientation was calculated to be 81% theoretically. Further washing experiments suggested that the nonspecific adsorption may be attributed to both the electrostatic attraction and the hydrophobic interaction.