The extremely halophilic bacterium, purple membrane producing Halobacterium halobium strain R1 were cultured in four liquid media which consist of different constituents. After the purple membrane is harvested by ultracentrification and purified by sucrose density gradient ultracentrification, and run on SDS-PAGE, the result of Coomassie blue staining showed different bR protein forms: three bands with molecule weight ranging from 26.0 to 27.5 kD in peptone medium, while only one band with MW 26.0 kD in other three media-complex, synthetic and artificial seawater media, which corresponded to the mature form in peptone medium. The result of Western blotting not only confirmed the different protein forms of Coomassie blue staining in the four media, but also gave additional bands that Coomassie blue can not detect due to its lower sensitivity: 1) in the complex, synthetic and artificial seawater media, a faint 28.0 kD band existed, while in the peptone medium it did not exist; and 2) in the four media, it appeared that a faint 23.0-24.0 kD band exited. The different bR protein forms of purple membrane which result from the difference of nutritional constituents in these four media might be caused by different precursor processing enzymes or different activities of precursor processing enzyme(s) under these different nutritional conditions.