The conformational propensity of the 20 naturally occurring amino acids was determined in aqueous 3- [N-morpholino]propane-sulfonic acid (MOPS) buffer, protein interiorlike [nonmicellar sodium dodecylsulfate (SDS)] and membrane-like environments (micellar SDS and lysophosphatidylglycerol/lysophosphatidylcholine micelles) using a single ''guest'' position in a polyalanine-based model host peptide (Ac-KYA 13 K-NH 2 ). This model system allows the intrinsic a-helical or b-sheet propensity of the amino acids to be determined without intra-and interchain side chain interactions. The overall environment dependence observed for the conformational propensity for the amino acids studied confirms the importance of determining propensity in lipidic environments to better elucidate the biological functions of proteins. The hydrophobic interactions between peptide side chains and lipids appeared to be the primary forces driving the conformational induction in lipidic environments of the model peptides studied. Finally, when comparing the results of these studies with those reported in the literature, the local environment was found to highly influence 65% of the 20 naturally occurring amino acids.