This invention relates to derivatives of perhydroisoindol of formula: ##STR1## in which the radicals R are hydrogen atoms or together form a bond, the symbols R' are phenyl radicals which can be substituted by a halogen atom or a methyl radical in position 2 or 3, X is an oxygen atom or an NH radical, R.sub.1 is optionally substituted phenyl, or cyclohexadienyl, naphthyl, or heterocyclyl, R.sub.2 is H, halogen, OH, alkyl, aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl, alkyloxy, alkylthio, acyloxy, carboxy, optionally substituted alkyloxycarbonyl, benzyloxycarbonyl, amino or acylamino, R.sub.3 is halogen or OH and R.sub.4 is H or halogen if R.sub.3 is halogen, in their isomer forms, or mixture thereof, and possibly also their salts when they exist, and preparation thereof. The derivatives of the invention are particularly interesting as P substance antagonist.