Abstract: 5-(2-methyl-2-thiol ethyl) hydantoin and derivatives thereof are useful in the treatment of evolutive chronic polyarthritis.

Abstract: Psychotropic composition comprising as an active constituent, a pharmaceutical composition, more particularly a psychotropic composition, characterized in that it comprises as an active constituent, a deuterated phenylhydantoin corresponding to the general formula ##STR1## wherein radicals R.sub.1 are identical or different and represent hydrogen or methyl, R.sub.2 is ethyl or a substituted or unsubstituted phenyl group, which is deuterated or not, R.sub.3 is hydrogen, halogen or a linear or ramified alkyl radical comprising 1 to 4 carbon atoms, a linear or ramified alkoxy radical comprising 1 to 4 carbon atoms, a trifluoromethyl, hydroxy, nitro or amino radical, X is an oxo, thio or methylene group and x is an integer of 1-5, one of its enantioners or one of its salts with a physiologically acceptable base, in combination with a pharmaceutically acceptable vehicle.