The importance of highly polyunsaturated fatty acids in health and development has been convincingly demonstrated by many studies over the past several decades. The mechanisms by which polyunsaturated lipid species might influence biological function at the molecular level are now attracting considerable attention. The G-protein-coupled receptor rhodopsin and docosahexaenoic acid, the dominant fatty acid in the retinal membrane, provide the best-studied example of protein function being influenced by lipid environment.