The invention relates to biologically active molecules, interacting with thrombin and inhibiting the same. The invention particularly relates to molecules of general formula:Y.sup.1--(NH--X.sup.1--C.dbd.O)--(NH--X.sup.2--C.dbd.C)--(NH--X.s- up.3--C.dbd.O)NH--X.sup.4--C.dbd.O)--(NH--X.sup.5--C.dbd.O)--(NH--X.sup.6-- -C.dbd.O)--Y.sup.2, in which Y.sup.1, Y.sup.2, and X.sup.1-6 have the meanings given in the description, N or C-terminal shortened variants of said compounds and the use thereof for the production of medicaments.