Cyclooxygenase (COX) is the key enzyme in the conversion of arachidonic acid to prostaglandins. COX has two isoforms: COX-1, the constitutively expressed form, and COX-2, the inducible form. Prostaglandins are mediators of many critical physiological and inflammatory responses, but little is known about their roles during a viral infection in the central nervous system (CNS). We used non-selective inhibitors of COX, aspirin and indomethacin, and a selective antagonist of COX-2, celecoxib, to study the role of prostaglandins in Vesicular Stomatitis Virus (VSV) induced encephalitis. We found that the inhibition of COX antagonizes VSV propagation both in vitro and in vivo. In addition, aspirin and celecoxib both prevented the disruption of the blood brain barrier in VSV-infected mice. In vitro experiments showed that the effect of COX inhibition was at least partially mediated by increased production of Nitric Oxide (NO), a molecule known to inhibit VSV replication. When NO production was inhibited by N(omega)-nitro-L-methyl-arginine-ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, the difference in viral titer between aspirin (or celecoxib)-treated and the control cells was abolished. VSV-infected mice treated with celecoxib expressed more NOS-1 and produced more NO in their CNS compared to the controls. Our data suggest that the product(s) of COX have antagonistic effect(s) on NO production in the mouse CNS.