The effect of flurbiprofen, a prostaglandin cycloxygenase inhibitor, on tooth movement was studied using New Zealand white rabbits. Under general anaesthesia, springs were ligated between the lower first molars and incisors resulting in approximation of these teeth. Experimental animals were matched to a control animal of the same sex and weight. Experimental animals were administered daily flurbiprofen (10 mg/Kg) via a catheter passed orally into the stomach. Control animals received the vehicle only. A pair of animals (experimental and matched control) was sacrificed after 3 and 10 days, and the remaining animals after 14 days. The movement of incisors and molars was measured directly, and movement between the first and second molars measured from radiographs. Osteoclast activity in the area of crestal bone adjacent and mesial to the first molar was examined histologically. Direct and radiographic measurements showed movement within the experimental and control groups, but no significant difference between them. However, the radiographic measurements showed a trend towards decreased tooth movement in the experimental animals. This observation, together with a significant decrease in the number of osteoclasts in the bone adjacent to the induced tooth movement in the experimental animals, suggests non-steroidal anti-inflammatory drugs can partially inhibit orthodontic tooth movement. The most likely mechanism is the inhibition of prostaglandin synthesis with a resultant inhibition of osteoclast activity and bone resorption. However these findings suggest other undefined mechanisms remain unaffected.