Fibrinogen fragment D prepared in the presence of calcium ions (fragment D[Ca++]) shows qualitatively similar cross-linking patterns with dimethyl suberimidate, dimethyl adipimidate and tetranitromethane. Fragment D prepared in the presence of EDTA (fragment D[EDTA]) gives a consistently different pattern with these reagents. In the case of fragment D[EDTA] there is much more intermolecular cross-linking suggesting that the loss of the C-terminus of the gamma-chain remnant results in fragment D adopting a more open conformation. Neither the addition of 2M urea nor EDTA to fragment D[Ca++] alters its cross-linking pattern suggesting that the proposed conformational change follows cleavage of a plasmin susceptible bond which is normally protected by the presence of calcium ions.