The recent marketing of two selective cyclooxygenase 2 (COX-2) inhibitors climaxes the first phase of an exciting and fast-paced effort to exploit a novel molecular target for nonsteroidal anti-inflammatory drugs (NSAIDs). Much has been written in the lay and scientific press about the potential of COX-2 inhibitors as anti-inflammatory and analgesic agents that lack the gastrointestinal side-effects of traditional NSAIDs. Although research on COX-2 inhibitors has focussed mainly on inflammation and pain, experimental and epidemiological data suggest that COX-2 inhibitors could be used in the treatment or prevention of a broader range of diseases. In this review, some key points and unresolved issues related to the discovery of COX-2 inhibitors, the kinetic and structural basis for their selectivity, and possible complications in their development and use will be discussed.