The present invention is based on the finding that the cis/trans isomerisation of secondary amide peptide bonds in oligo- and polypeptides can be catalytically promoted. This catalysis is effected by enzymes which are hereinafter called "secondary amide peptide bond cis/trans isomerases (APIases). It can be assumed that the APIase activity plays a central role in a number of pathophysiological processes. Thus, the invention relates to pharmaceutical compositions comprising substances which inhibit APIase activity.