A pyrazine derivative of the following formula (I): ##STR00001## wherein R.sup.1 is hydrogen or optionally substituted lower alkyl; X is hydrogen, halogen, hydroxy, cyano, acyl, or amino, aryl, heterocyclic group or the like; Y is hydrogen, halogen, hydroxy, acyl, amino, or the like; Z is aryl or heteroaryl, each of which is optionally substituted; or a salt thereof. The pyrazine compound (I) and a salt thereof of the present invention are adenosine antagonists and are useful for the prevention and/or treatment of depression, dementia (e.g. Alzheimer's disease, cerebrovascular dementia, dementia accompanying Parkinson's disease, etc.), Parkinson's disease, anxiety, pain, cerebrovascular disease (e.g. stroke, etc.), heart failure and the like.