The invention relates to the use of aids of the general formula ##STR1## in which B denotes a basic amino acid, A/B denotes an acidic or basic amino acid, X denotes a neutral and hydrophilic amino acid, L denotes a lipophilic neutral amino acid, and R denotes hydrogen or an acyl radical, or the physiologically tolerated salts thereof, for promoting the absorption of peptides and proteins on administration onto the mocosa, as well as to pharmaceutical compositions which contain a pharmacologically effective amount of one or more peptides or proteins as well as an aid of the abovementioned formula.