A fibrin sealant comprises a mixture of first microparticles that comprisefibrinogen, second microparticles thatcomprise thrombin, and additive material. The additive material may beparticulate, and may be, for instance, a biocompatible,wa-ter- absorbent, material, a biocompatible, water-swellable material, abiocompatible, water-insoluble material, a polysaccharide orsilica.