Dextran sulphate is used to potentiate C1-esterase inhibitor selectively with respect to inhibition of complement and coagulation, but not with respect to inhibition of the contact and fibrinolytic systems. The C1-esterase inhibitor to be potentiated by the dextran sulphate may be endogenous C1-esterase inhibitor, or exogenous C1-esterase inhibitor which is to be administered together with or separate from the dextran sulphate. Use of the dextran sulphate, alone or together with C1-esterase inhibitor, in prophylactic or therapeutic treatment of inflammatory conditions, such as sepsis and myocardial infarction.