The effect of melittin on lipid order in dimyristoylphosphatidylcholine bilayers was investigated by Raman spectroscopy and fluorescence anisotropy with diphenylhexatriene as fluorescent probe. In the fluid lipid phase, the Raman results indicated a slight increase in the conformational order of the lipid chains, and the fluorescence anisotropy results indicated a considerable increase in the rigid-body orientational order of the lipid chains. These results were contrasted with the reported decrease in the 2H NMR order parameter. A consistent interpretation of the complete set of exptl. data is presented according to which proteins induce a tilt of the preferred axes of lipid orientation and increase the orientational order with respect to these axes. The values of the tilt angle and the orientational order parameter at the surface of proteins are detd. from the exptl. data within a continuum model of lipid-protein interaction. These values were obtained for melittin, Ca2+,Mg2+-ATPase, and cytochrome c oxidase, suggesting that membrane proteins affect the lipid order in the same way. [on SciFinder (R)]