DMPX (3,7-dimethyl-1-propargylxanthine) is a caffeine analog which displays affinity for A<sub>2</sub> adenosine receptors, in contrast to the A<sub>1</sub> subtype receptors. DMPX had 28 times and 15 times higher potency than caffeine in blocking, respectively, the peripheral and central effects of the adenosine agonist NECA. The locomotor stimulation caused by DMPX (ED<sub>50</sub> 10 ümol/kg) was similarly higher than caffeine.