Comparative computer modeling of the X-ray crystal structures of cyclooxygenase isoforms COX-1 and COX-2 has led to the design of COX-2 selectivity into the nonselective inhibitor flurbiprofen. The COX-2 modeling was based on a postulated binding mode for flurbiprofen and took advantage of a small alcove in the COX-2 active site created by different positions of the Leu384 sidechain between COX-1 and COX-2. The design hypothesis was tested by synthesis and biological assay of a series of flurbiprofen analogs, culminating in the discovery of several inhibitors having up to 78-fold selectivity for COX-2 over COX-1.