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 2 are phenyl radicals which can be substituted by a halogen atom or a methyl radical in position 2 or 3 , r 3 is a halogen atom or a hydroxy radical , r 4 is h or halogen if r 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 .