The fibrinolytic and anticoagulant activities of heparan sulphate (HS) and dermatan sulphate (DS) were compared with those of heparin using in vitro tests. Our results demonstrate that HS has higher profibrinolytic activity than heparin and DS. Although 50 times less potent than heparin in inhibiting factor IIa, HS is three times more active than DS. The action of HS resides in HCH-mediated factor IIa inhibition combined with an ATIII-mediated inhibition. DS has no action on ATIII-mediated inhibition of factor IIa. The comparison of the anticoagulant activities of the three compounds confirmed the very limited anticoagulant effect of both HS and DS in comparison with heparin.