This study provides a complete overview on all possible helical- folding patterns, their stabilities, and their detailed molecular structure in the novel foldamer class of alpha,beta-hybrid peptides on the basis of ab initio molecular orbital (MO) theory. The results indicate a considerable intrinsic potential of backbone folding. As found for other peptide foldamers, representatives of mixed or beta-helices are most stable in more apolar media, whereas polar environments favor the helices with the hydrogen bonds pointing in only one direction. The theoretical results confirm the hydrogen-bonding patterns found in the first experimental studies on these hybrid peptides. Selecting special backbone substitution patterns, the secondary structure potential of the alpha,beta-hybrid peptides could be of great importance for a rational peptide and protein design.