The disulphide peptides of flour have been separated into acidic (glutathione) and basic peptides, and their effects on the rheological properties of dough have been investigated. the only peptide normally present in flour to have marked activity in dough was glutathione. The other disulphide peptides of flour were only slightly active in that their sole effect was to diminish the tolerance of the dough to prolonged mixing. Their lack of activity probably results from their disulphide groups being non‐reactive at the pH values found in dough. the same peptides in the thiol form were slightly more active in that they decreased development time and maximum resistance. All types of thiols tested were active in dough, but of the disulphides tested, only the acidic peptides GSSG (oxidised glutathione) and bis‐γ‐glutamylcystine had significant activity. Possible modes of action of disulphide peptides in dough are discussed. Copyright © 1969 John Wiley & Sons, Ltd