Asthma is a chronic inflammatory disease, and its prevalence is relatively high among children. Optimal management of asthma often requires longterm pharmacotherapy; however, the effects of these medications on orthodontic treatment is uncertain. We evaluated the effects of the leukotriene LTD 4 receptor antagonist montelukast on orthodontic tooth movement in an animal model. Eight mongrel dogs were given montelukast for periods up to 4 weeks. An orthodontic force of 150-200 g was applied to move the second and fourth premolars toward the site of the extracted third premolar. The distance between premolars was measured at baseline and at weeks 1, 2, and 4. Histological examination with hematoxylineosin staining was used to evaluate osteoclast activity. A slight delay in orthodontic movement and decreased osteoclast activity were observed in the montelukasttreated group, as compared with untreated controls. However, the differences were not statistically significant (P > 0.05). Our findings suggest that montelukast use will not interfere with orthodontic treatment of asthma patients. However, these findings require confirmation in clinical studies.