It is well known that the adenosine antagonist caffeine increases the spontaneous motor activiy while adenosine agonists reduce it. The aim of this work was to analyze the role of adenosine ligands on the circadian motor activity regulation through the dopaminergic system in both immature and adult rats. The homovanillic acid (HVA) levels measured by HPLC in striatum were used as index of dopamine metabolism. In immature rats during the inactive period (daytime), the adenosine A1 agonist R-PIA (0.1 mg/kg, 1h) showed inhibitory effects on dopamine metabolism (37%), while the adenosine A2 agonist CGS-21680 (1 mg/kg, 1h) did not cause effects. Oppositely, during the active period (nighttime), both A1 and A2 agonists displayed stimulatory effects on dopamine metabolism (65% and 44% respectively). In adult rats, a lack of A1 agonist effects were observed independently of the active-inactive motor period; while the A2 agonist showed stimulatory effects on dopamine metabolism only during the active period (30%). The non selective adenosine antagonist caffeine (50 mg/kg, 1 h) always increased the dopamine metabolism, either in immature and adult rats when it was administered during light time (182% and 67%, respectively) as well as during dark period (65% and 48%, respectively). Alltogether, the data support a role of dopaminergic system on adenosine regulation of the circadian activity cycle. Thus, the increase of adenosine levels produced as a consequence of the activity of rats along the nighttime support the depressed motor activiy at the beggining of the daytime.