© 2021 by Wroclaw Medical University.Background. Orthodontic tooth movement (OTM) is a complex phenomenon mediated by cytokines, of which interleukin-1 beta (IL-1β) is potently involved in the remodeling of the periodontal ligament (PDL) and bone. Whether the pattern of IL-1β release differs at the sides of tension and compression is not yet clarified. Objectives. The aim of the present study was to evaluate the level of IL-1β and the ratio of IL-1β to interleukin-1 receptor antagonist (IL-1RA) in gingival crevicular fluid (GCF) at the tension and compression sides during orthodontic canine retraction. Material and methods. Seventeen patients scheduled for orthodontic treatment with bilateral extrac-tion of maxillary first premolars and canine retraction were enrolled. Tooth 2.3 was retracted, teeth 1.3 and 3.3 served as controls. Gingival crevicular fluid samples were collected from the tension and compression sides of each tooth at baseline (before the 1st activation – day 0) and at days 2 and 7, and then again before the 2nd activation (day 28) and at days 30 and 35. The levels of IL-1β and IL-RA were evaluated with the enzyme-linked immunosorbent assay (ELISA). Results. After the 1st activation, a statistically significant increase in the level of IL-1β was observed at teeth 2.3 (p < 0.03 mesially and p < 0.05 distally) and 1.3 (p < 0.05 mesially and distally), both at the tension and compression sides. The 2nd activation resulted in a gradual increase in the IL-1β level at both canines; however, statistical significance was reached only for tooth 2.3 (p < 0.05 mesially and p < 0.02 distally). In terms of the IL-1β/IL-1RA ratio, a significant increase was observed only at the compression side of the experimental tooth (p < 0.01). Conclusions. An increase in the IL-1β level in GCF was observed both at the tension and compression sides of the actively retracted canine 2.3 as well as the contralateral canine 1.3; a significant rise in the IL-1β/IL-1RA ratio was noted only at the compression ...