The present invention describes pyridazinone compounds of formula I ##STR00001## which are cyclooxygenase (COX) inhibitors, and in particular, are selective inhibitors of cyclooxygenase-2 (COX-2), COX-2 is the inducible isoform associated with inflammation, as opposed to the constitutive isoform, cyclooxygenase-1 (COX-1) which is an important "housekeeping" enzyme in many tissues, including the gastrointestinal (GI) tract and the kidneys. The selectivity of these compounds for COX-2 minimizes the unwanted GI and renal side-effects seen with currently markered non-steroidal anti-inflammatory drugs (NSAIDs).