Amidine compounds of formula (I) ##STR1## and the pharmaceutically acceptable acid addition salts thereof are novel and are of use as anti-trypsin, anti-plasmin, anti-kallikrein, anti-thrombin and anti-complement agents which may be administered orally. These amidine compounds can be produced by the reaction between a carboxylic acid compound of formula (II) ##STR2## or a reactive intermediate thereof and 6-amidino-2-naphthol of formula (III) ##STR3## or preferably an acid addition salt thereof.