The present invention relates to prodrugs of pharmacologically active five-membered heterocyclic amidines from which are produced in vivo compounds which are competitive inhibitors of trypsin-like serine proteases, in particular thrombin and kininogenases such as kallikrein, to the preparation thereof and to the use thereof as medicines. The invention also relates to pharmaceutical compositions which comprise the prodrugs of the active compounds as ingredients, and to the use of the compounds as thrombin inhibitors, anticoagulants and as antiinflammatory agents.