Energy calculations have been carried out for several oligomeric peptides derived from beta-methyl alpha-L-aspartate, beta-ethyl alpha-L-aspartate, and beta-propyl alpha-L-aspartate. Self-consistent field calculations have revealed the favored helix sense for such compounds, while self-consistent reaction-field calculations have indicated the influence exerted by the solvent on their conformational preferences. The right-handed alpha-helix was found to be the most favored conformation for both the ethyl and propyl derivatives. On the contrary, the conformation preferred by the methyl derivatives was the left-handed omega-helix. The influence of the interactions between the amide and ester groups on the helical sense preferences displayed by these compounds are discussed.