n 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 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 ; ## str2 ## wherein r 1 and r 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 ## 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 2 , monosubstituted methylene ## str4 ## wherein r 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 4 r 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 6 is an alkyl group of not more than 10 carbon atoms , acyl substituted imino ## str8 ## wherein r 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 .