This study investigates the effect of an orthodontic force on pulpal respiration in the human premolar. The participants in this study required the removal of four first premolars for orthodontic treatment. After written consent was obtained, these teeth were used in the following manner. Randomly, the premolars on one side of the mouth were designated as experimental and the premolars on the opposing side served as controls. The four teeth were removed following a 3-day application of an orthodontic force. The pulp tissue was then extirpated and used for the investigation. A radioactively labeled carbon dioxide production system was used to evaluate the effect on pulpal respiration of the orthodontic force. It is thought that this method has been proved to provide a viable and sensitive biochemical analysis of tissue respiration on very small samples over short observation periods. The data were collected and prepared for statistical analysis. This investigation demonstrated that the pulp tissue respiration in seventeen subjects was depressed an average of 27% as a result of orthodontic force application. A positive correlation between the age of the participant and the amount of tissue respiratory depression was also demonstrated. It was therefore concluded that orthodontic forces of very short duration do cause biochemical and biologic pulpal tissue alterations and that orthodontic forces may be less biologically safe as the age of the patient increases.