Langmuir-Blodgett (LB) films of bovine rhodopsin were prepared and studied using FTIR spectroscopy in the region between 700 and 4000 cm(-1). A substantial decrease of lipids was found in LB films compared to spread films. This suggested that most of the phospholipids surrounding the protein were expelled during the film compression. Moreover, the relatively high amide II/amide I ratio found in LB films indicates that the or-helices are oriented perpendicular to the film plane. The secondary structure of rhodopsin was estimated from the amide I spectrum. The content of a-helical structure obtained for rhodopsin in the spread and in the LB films was 70 and 67%, respectively, while that of P-sheets was about 13% either in LB or in spread films. These results suggest that bovine rhodopsin, although losing most of its surrounding lipids when assembled in LB films, preserves its orientation and its secondary structure.