Compounds of formula (I) ##STR00001## wherein: X is N; R.sub.1 is C.sub.1 C.sub.6 linear or branched alkyl or C.sub.1 C.sub.6 linear or branched alkenyl; R.sub.2 is hydrogen, C.sub.1 C.sub.6 linear or branched alkyl or C.sub.1 C.sub.6 linear or branched alkenyl, C.sub.6 C.sub.14 aryl or C.sub.6 C.sub.14 aryl(C.sub.1 C.sub.6) linear or branched alkyl or C.sub.6 C.sub.14 aryl(C.sub.1 C.sub.6) linear or branched alkenyl, with the aryl group optionally substituted by one or more substituents, either the same or different, selected from the group consisting of halogen, hydroxy, C.sub.1 C.sub.6 alkoxy linear or branched or C.sub.114 C.sub.6 alkenyloxy linear or branched, amino, optionally mono- or disubstituted with C.sub.1 C.sub.6 linear or branched alkyl; R.sub.3 is NH.sub.2, NHR.sub.4; R.sub.4 is C.sub.1 C.sub.6 alkyl or C.sub.1 C.sub.6 hydroxyalkyl, C.sub.1 C.sub.3 alkoxyalkyl, amino(C.sub.1 C.sub.6)alkyl, where the amino group is optionally substituted with one or two C.sub.1 C.sub.3 linear or branched alkyl groups, or with one or two C.sub.2 C.sub.3 alkenyl groups C.sub.6 C.sub.14 aryl or C.sub.6 C.sub.14 aryl(C.sub.1 C.sub.6)alkyl, with the aryl group optionally substituted by one or more substituents, either the same or different, selected from the group consisting by halogen, hydroxy, C.sub.1 C.sub.6 alkoxy linear or branched or C.sub.1 C.sub.6 alkenyloxy linear or branched, amino, mono- or di-substituted with C.sub.1 C.sub.6 alkyl linear or branched or C.sub.1 C.sub.6 alkenyl linear or branched; and their pharmaceutically acceptable salts. These compounds are antagonists of the adenosine A.sub.2a receptor and useful as medicaments, in particular for the treatment of Parkinson's disease.