Peptide formation by the recently discovered salt-induced mechanism, the simplest possible prebiotic peptide generation process so far, has been studied by the example of some amino acids known to form by Miller or Fischer-Tropsch mechanisms in simulated primitive atmosphere experiments. Valine and aspartic acid readily form peptides with glycine; self-condensation is observed for all acids except valine. Several findings give further indications towards the possible prebiotic relevance of the reaction: the observed preferential formation of peptide linkages, the shift from ‘nature-irrelevant’ to ‘nature-relevant’ peptide bonds in the presence of Cu(II) and the long conservation of optical purity in the reaction system. Additional data confirming the proposed reaction mechanism were obtained.