We have identified and characterised a novel member of the PDE7 family of cyclic nucleotide phosphodiesterases (PDE), which we have designated PDE7B. Mouse and human full-length cDNAs were isolated encoding a protein of 446 and 450 amino acids, respectively. The predicted protein sequence of PDE7B showed highest homology (70% identity) to that of PDE7A. Northern blot analysis identified a single 5.5-kb transcript with highest levels detected in brain, heart, and liver. Kinetic analysis of the mouse and human purified recombinant enzymes show them to specifically hydrolyse cAMP with a Km of 0.1 and 0.2 microM respectively. Inhibitor studies show sensitivity to dipyridamole, IC50 of 0.51 and 1.94 microM, and IBMX, IC50 of 3.81 and 7.37 microM, for the mouse and human enzymes, respectively. This shows that dipyridamole is not selective for cGMP over cAMP PDEs as previously believed. Other standard PDE inhibitors including zaprinast, rolipram, and milrinone do not significantly inhibit PDE7B.