This study was undertaken to evaluate the scavenging activity for reactive oxygen species (ROS) and reactive nitrogen species (RNS) by several nonsteroidal anti-inflammatory drugs (NSAIDs), namely indole derivatives (indomethacin, acemetacin, etodolac), pyrrole derivatives (tolmetin and ketorolac), and an oxazole derivative (oxaprozin). The inhibition of prostaglandin synthesis constitutes the primary mechanism of the anti-inflammatory action of these drugs. Nevertheless, it has been suggested that the anti-inflammatory activity of NSAIDs may be also partly due to their ability to scavenge ROS and RNS and to inhibit the respiratory burst of neutrophils triggered by various activator agents. Thus, the scavenging activity of these NSAIDs was evaluated against an array of ROS (O(2)(-), HO, HOCl, and ROO) and RNS (NO and ONOO(-)) using noncellular in vitro systems. The results obtained demonstrated that tolmetin, ketorolac, and oxaprozin were not active against O(2)(-), while acemetacin, indomethacin, and etodolac exhibited concentration-dependent effects. Oxaprozin was also the least active scavenger for HO, among all the tested NSAIDs shown to be active. The scavenging effect for HOCl was not observed for any of the tested NSAIDs. The ROO was effectively scavenged by etodolac, with the other tested NSAIDs being much less active. NO and ONOO(-) were scavenged by all the tested NSAIDs. These effects may strongly contribute to the anti-inflammatory therapy benefits that may be attained with some of the studied NSAIDs.