A derivative of p-guanidinobenzoic acid of the general formula (IA): ##STR1## wherein Y represents an oxygen atom or a sulfur atom and (a) when Y is an oxygen atom, (R.sup.1).sub.m is selected from the group consisting of: 5-(4-guanidinobenzoyloxy)-3-methoxymethyl, 3,5-dicarboxy, 3,5-bis(isopropoxycarbonyl), 3,5-bistrifluoromethyl, 3-acetyl, 3,5-bis(N-ethylcarbamoyl), and 3,5-bis(N-propylcarbamoyl);(b) when Y is a sulfur atom, (R.sup.1).sub.m is selected from the group consisting of: 2-methyl, 3-methyl, 4-fluoro, 2-chloro, 3-chloro, 2,5-dichloro 2,6-dichloro, 3,4-dichloro, 2-bromo, 2-methoxycarbonyl, and 4-(N,N-diethylaminosulfonyl);or an acid addition salt of said derivative. A method for the treatment or prevention of diseases induced by abnormal enhancing of degradation of proteins by the action of elastase in mammals subject to or suffering therefrom, including the step of administering an effective amount of a p-guanidinobenzoic acid as described herein, is also disclosed.