Materials and Methods: A total of 30 Wistar rats were divided randomly into test and control groups. Starting from the first 3 days, the rats in the test group were injected intra-peritoneally by 2 mg ovalbumin as allergen and 0.5 mg Alume as adjuvant. Afterward only allergen was injected once a week. The control group was injected by normal saline. After 21 days, Wistar immunoglobulin E was measured and peripheral matured eosinophil was counted. A total of 50 g nickel-titanium closed coil spring was ligated between right incisor and first molar. All animals were sacrificed after 14 days. The mesial root of the right and left first molar was dissected in a horizontal plane. The specimens were divided into four groups considering whether force and/or ovalbumin was applied or not. Root resorption was measured and compared among these groups. Repeated measures analysis of variance (ANOVA), and Bonferoni tests were used to analyze the data. The level of significance was determined at 0.05. 

  Results: In general, the differences were insignificant (P > 0.05). As the only exception, the group in which both ovalbumin and force were applied had significantly more root resorption than the group in which neither force nor ovalbumin was applied (P < 0.001). 

  Conclusion: Allergy may increase the susceptibility to root resorption. Application of light force, periodical monitoring of root resorption and control of allergy are advisable.