We evaluated the potential of [(11)C]MPDX as a radioligand for mapping adenosine A(1) receptors in comparison with previously proposed [(11)C]KF15372 in cat brain by PET. Two tracers showed the same brain distribution. Brain uptake of [(11)C]MPDX (Ki = 4.2 nM) was much higher and washed out faster than that of [(11)C]KF15372 (Ki = 3.0 nM), and was blocked by carrier-loading or displaced with an A(1) antagonist. The regional A(1) receptor distribution evaluated with kinetic analysis is consistent with that previously measured in vitro. [(11)C]MPDX PET has a potential for mapping adenosine A(1) receptors in brain.