Abstract This paper deals with the synthesis of N α-(β-naphthylsulfonylaminoglycyl)- argininamide compounds and the results of a pharmacological study (in vitro and in vivo). No thrombin inhibition was obtained with N α-arylsulfonyl-aminoalkyl-(4-amidinophenyl)- alaninamide compounds in which the 4-amidinophenylalanyl residue was substituted by an arginyl residue.