The invention provides novel pyrimidone compounds exhibiting excellent antagonism against adenosine receptors (A.sub.1, A.sub.2A, and A.sub.2B receptors), particularly, compounds represented by the general formula (1), salts thereof, or solvates of both: (1) wherein R.sup.1 and R.sup.2 are each independently hydrogen, C.sub.1-6 alkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.3-8 cycloalkyl, C.sub.3-8 cycloalkenyl, a 5- to 14-membered nonaromatic heterocyclic group, a C.sub.6-14 aromatic hydrocarbon group, a 5- to 14-membered aromatic heterocyclic group, C.sub.1-6 acyl, or C.sub.1-6 alkylsulfonyl; R.sup.3 is hydrogen, C.sub.1-6 alkyl, C.sub.2-6 alkenyl, or C.sub.2-6 alkynyl; R.sup.4 is a C.sub.6-14 aromatic hydrocarbon group; a 5- to 14-membered aromatic heterocyclic group, or a 5- to 14-membered nonaromatic heterocyclic group having at least one unsaturated bond; and R.sup.5 is a C.sub.6-14 aromatic hydrocarbon group or a 5- to 14-membered aromatic heterocyclic group (with the proviso that every group except hydrogen may be substituted).