beta-Hexapeptides and a beta-dodecapeptide with sequences contg. two different types of beta-amino acids, aliph. proteinaceous side-chains in 2- or 3-position, were studied with CD and NMR measurements. With one exception, the secondary structures formed by these beta-peptides differ from those of isomers studied previously. Detailed NMR anal. of the beta-hexapeptide with alternating beta2,beta3-building blocks, and mol.-dynamics simulations revealed a min. energy conformation which is described as a novel irregular helix contg. 10- and 12-membered H-bonded rings.