In previous work we have shown that some new regenerating agents (RGTAs), molecules which correspond to some dextran derivatives (DxD) containing defined amounts of carboxymethyl (CM), benzylamide (B) and benzylamide sulfonate (BS) groups, were able to stimulate tissue repair when applied at the site of injury. Based on in vitro studies showing that these DxD could interact and protect heparin binding growth factors (HBGFs), we postulated that DxD could also act in vivo by protecting endogenously released HBGFs against protease degradation. We now present data demonstrating that human plasmin (HP1), one of the known proteases involved in extracellular matrix remodelling and in the local activation of some growth factors is specifically inhibited by some specific DxD. The most efficient compounds for inhibiting the amidolytic activity were substituted by all functions with IC50 at 0.26 microM for RGTA11 (a DxD obtained from a 40,000 Da dextran containing 110% of CM, 2.5% of B and 36.5% of BS units and with IC50 at 1.1 microM for RGTA10 (derived from 10,000 Da dextran and containing 110% of CM, 0% of B and 27.3% of BS). Compounds which were substituted with only one or two functions were less effective. The degradation of FGF-2 by HP1 was analyzed by SDS-PAGE and by measuring its residual growth promoting activity using a bioassay on human skin fibroblasts. In this assay, RGTA11 at a concentration of 1 microM could inhibit by 80-100% FGF-2 degradation induced by HP1 treatment. In conclusion, the inhibitory activity of some DxD towards HP1 as well as the ability of these DxD to protect FGF-2 against this proteinase could partially explain its beneficial influence on extracellular matrix remodelling following tissue injury.