OBJECTIVES - To test the hypothesis that during root resorption, organic matrix proteins and cytokines from the surrounding bone and dentin are released into the gingival crevice. MATERIAL AND METHODS - Subjects with mild (<2 mm loss) and severe root resorption (>2 mm) were identified. Control group subjects with no loss of root structure or undergoing orthodontic treatment were also identified. Gingival crevicular fluid (GCF) was collected non-invasively from the mesial and distal sides of each of the four upper incisors by using filter paper strips. The eluted GCF was used for analysis using western blot and enzyme-linked immunosorbent assay (ELISA) techniques. Antibodies used were against osteopontin (OPN), (osteoprotegerin) OPG, and receptor activator of nuclear factor kappa B ligand (RANKL). RESULTS - Western blot analysis showed differential expression of OPN, OPG, and RANKL in the control and root resorbed subjects. However, processed forms of these proteins were only observed in the root resorbed subjects. Results from ELISA with OPG antibodies revealed a difference in OPG concentration between the control and root resorption groups. ELISA results with RANKL antibodies did show a statistically significant difference between the control group and the two study groups. The ratio RANKL/OPG was statistically higher in subjects with severe root resorption than in the control subjects. CONCLUSIONS - Preliminary results confirm the presence of matrix proteins and cytokines in the GCF of root resorbed subjects. Further, OPG was locally present in excess amounts over RANKL and an increased RANKL/OPG in the study groups could be correlated with an increased bone resorption activity during orthodontic tooth movement.