Abstract: The present invention concerns new 5-monoaryl as.-triazin-3-ones substituted in 2-position, a method of preparing them, and their use as medicaments.The compounds according to the present invention have general formula (I) ##STR1## in which: the bond represented by a dashed line indicates the presence of an optional double bond;A represents a direct N--C bond, a straight or branched C.sub.1 to C.sub.5 alkylene, possibly substituted one or more times by --COOR' or by Ar;R represents --H, --OH, ##STR2## R' represents --H, --OH, straight or branched C.sub.1 to C.sub.7 alkyl, --NH.sub.2 ;Ar represents an aromatic ring having 5 or 6 members possibly containing a heteroatom such as O, N, S and possibly substituted one or more times by a radical selected from among --OH, C.sub.1 to C.sub.4 alkyl, C.sub.1 and C.sub.4 alkoxy, halogen, --CF.sub.3, acetonyloxy, ##STR3## and .gamma.-butyrolactone; as well as their pharmaceutically acceptable salts.