A series of N"-(arylsulfonyl)-L-arginine amide derivatives having carboxamide N- substituents with a carboxyl group was prepared and tested as inhibitors of the clotting activity of thrombin. The most inhibitory compounds were obtained when a carboxyl group was introduced into the carbon next to the amide nitrogen of Nu-(arylsulfonyl)-L-arginine amide derivatives, eg, N'-(arylsulfonyl)-L-arginyl-N-butyl-, N-(methoxyethy1)-or N-( ...