Owing to their multiple side effects, the use of steroidal drugs is becoming more and more controversial, resulting in an increasing need for new and safer anti-inflammatory agents. In the inflammatory process, reactive oxygen species produced by phagocytic cells are considered to play an important role. We showed that apocynin (4'-hydroxy-3'-methoxy-acetophenone or acetovanillone), a non-toxic compound isolated from the medicinal plant Picrorhiza kurroa, selectively inhibits reactive oxygen species production by activated human neutrophils. Apocynin proved to be effective in the experimental treatment of several inflammatory diseases such as arthritis, colitis and atherosclerosis. These features suggest that apocynin could be a prototype of a novel series of non-steroidal anti-inflammatory drugs (NSAIDs). So far, apocynin is mainly used in vitro to block NADPH oxidase-dependent reactive oxygen species generation by neutrophils. In order to get a better insight in what chemical features play a role in the anti-inflammatory effects of apocynin, a structure-activity relationship study with apocynin analogs was performed. We show here that especially substances with an additional methoxy group at position C-5 display enhanced anti-inflammatory activity in vitro. Our approach may lead to the development of more effective anti-inflammatory agents which are safe and which lack the side effects of steroids.