N.sup.2 -dansyl-L-arginine esters and amides having the formula ##STR1## or the acid addition salts thereof with a pharmaceutically acceptable acid, wherein R is selected from the group consisting of (1) alkoxy, alkenyloxy, alkynyloxy, and cycloalkoxy, respectively, containing not more than 10 carbon atoms, aralkyl of not more than 15 carbon atoms, tetrahydrofurfuryloxy, and alkoxy of not more than 10 carbon atoms substituted with an alkoxy group of not more than 10 carbon atoms, halogen or nitro; (2) ##STR2## wherein R.sub.1 and R.sub.2 are members selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, alkenyl, and alkyl, wherein said member has no more than 10 carbon atoms, and wherein said alkyl may be substituted with a member selected from the group consisting of alkoxy, alkoxycarbonyl, arylcarbamoyl, acyl, acyloxy, N,N-polymethylenecarbamoyl, respectively, containing not more than 10 carbon atoms, and carboxyl; and (2) ##STR3## wherein Z is a divalent group containing up to 10 carbon atoms, which consists of more than one group selected from the group consisting of methylene --CH.sub.2, monosubstituted methylene ##STR4## wherein R.sub.3 is selected from the group consisting of alkyl, acyl, alkoxy, and alkoxycarbonyl, respectively, containing not more than 10 carbon atoms, and carbamoyl, and disubstituted methylene ##STR5## wherein R.sub.4 R.sub.5 are alkyl groups of not more than 10 carbon atoms, and which may further contain at least one member selected from the group consisting of oxy--O--, thio --S--, cycloalkylene of not more than 10 carbon atoms, imino ##STR6## alkyl substituted imino ##STR7## wherein R.sub.6 is an alkyl group of not more than 10 carbon atoms, acyl substituted imino ##STR8## wherein R.sub.7 is an alkyl group of not more than 10 carbon atoms, phenylene ##STR9## and carbonyl ##STR10## which completes the ring together with the said methylene, mono-substituted methylene or disubstituted methylene.