Human pS2 (trefoil factor family 1, TFF1), a 60‐amino acid member of the trefoil peptide family, forms dimers via Cys⁵⁸ and may stimulate gut repair. The effects of dimeric pS2‐TFF1 and monomeric pS2‐TFF1 (Cys⁵⁸ replaced by Ser⁵⁸) were compared in models of wound healing. Rats given dimeric pS2‐TFF1 at 25 and 50 μg/kg per h had 50 per cent and 70 per cent reduction in gastric damage induced respectively by indomethacin (20 mg/kg subcutaneously) and restraint (P<0·01). Monomeric pS2‐TFF1, at the same doses, was significantly less effective at reducing injury (about half the amount of protection, P<0·01 vs. same doses of dimeric). The rate of migration of cells at the leading edge of wounded monolayers of the human colonic cell line HT29 was increased by addition of dimeric or monomeric forms of pS2‐TFF1 (0·65–325 μg/ml). Dimeric pS2‐TFF1 had a greater effect than the monomeric form at all doses tested (P<0·05). Cell migration induced by pS2‐TFF1 was blocked by a pS2‐TFF1 antibody, but not by a transforming growth factor β neutralizing antibody. pS2‐TFF1 did not influence cell proliferation as assessed by thymidine incorporation. The increased biological effects of dimeric pS2‐TFF1 might be due to direct interaction of Cys⁵⁸ with a putative trefoil receptor or, more likely, dimerization of pS2‐TFF1 might stabilize the interaction with its receptor. This may involve a bivalent interaction of residues on the surfaces of the two trefoil domains. © 1998 John Wiley & Sons, Ltd.