Eicosanoids play key roles in many physiologic and disease processes, and their regulation by nonsteroidal anti-inflammatory drugs (NSAIDs) is critical to many therapeutic approaches. These autacoids are rapidly inactivated by specific enzymes such as 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and 15-oxoprostaglandin 13-reductase/leukotriene B-4 12-hydroxydehydrogenase (PGR/LTB4DH) that act on main series of eicosanoids (i.e., leukotrienes, prostaglandins), and recently found to act in lipoxin inactivation. Here, a panel of NSAIDs was assessed to determine each compound's ability to inhibit eicosanoid-directed activities of either the recombinant 15-PGDH or the PG-LXR/LTB4DH. The recombinant 15-PGDH that acts on both prostaglandin E-2 (PGE(2)) and lipoxin A(4) (LXA(4)) was not significantly inhibited by the NSAIDs tested. In contrast, several of the widely used NSAIDs were potent inhibitors of the PG-LXR/LTB4DH that metabolizes 15-oxo-PGE(2), and LTB4 as well as 15-oxo-LXA(4). Diclofenac and indomethacin each inhibited PG-LXRJLTB(4)DH-catalyzed conversion of 15-oxo-PGE, to 13,14-dihydro-15-oxo-PGE, by 70 and 95%, respectively. Also, a COX-2 inhibitor, niflumic acid, inhibited the PG-LXR/LTB4DH eicosanoid oxidoreductase (EOR) by 80% while other COX-2 inhibitors such as nimesulide and NS-398 did not inhibit this enzyme. These results indicate that certain clinically useful NSAIDs such as diclofenac and indomethacin, in addition to inhibiting cyclooxygenases (1 and 2), also interfere with eicosanoid degradation by blocking PG-LXR/LTB4DH (EOR) and are members of a new class of dual cyclooxygenase (COX)-EOR inhibitors. Moreover, they suggest that the impact of NSAIDs, on PG-LXR/LTB4DH activities as targets in the local tissue regulation of eicosanoid-mediated processes should be taken into account.