AIM: To assess the effects of mastic administration on cytokine production of circulating mononuclear cells of patients with active Crohn’s disease (CD). METHODS: The study was conducted in patients with established mildly to moderately active CD, attending the outpatient clinics of the hospital, and in healthy controls. Recruited to a 4 wk treatment with mastic caps (6 caps/d, 0.37 g/cap) were 10 patients and 8 controls, all of who successfully completed the protocol. Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), macrophage migration inhibitory factor (MIF) and intracellular antioxidant glutathione (GSH) were evaluated in peripheral blood mononuclear cells (PBMC) before and after treatment. RESULTS: Treating CD patients with mastic resulted in the reduction of TNF-α secretion (2.1 ± 0.9 ng/mL vs 0.5 ± 0.4 ng/mL, P = 0.028). MIF release was signif icantly increased (1.2 ± 0.4 ng/mL vs 2.5 ± 0.7 ng/mL, P = 0.026) meaning that random migration and chemotaxis of monocytes/macrophages was inhibited. No signifi cant changes were observed in IL-6, MCP-1 and GSH concentrations. CONCLUSION: This study shows that mastic acts as an immunomodulator on PBMC, acting as a TNF-α inhibitor and a MIF stimulator. Although further double-blind, placebo-controlled studies in a large number of patients is required to clarify the role of this natural product, this f inding provides strong evidence that mastic might be an important regulator of immunity in CD. AIM: To assess the effects of mastic administration on cytokine production of circulating mononuclear cells of patients with active Crohn’s disease (CD). METHODS: The study was conducted in patients with established mildly to moderately active CD, attending the outpatient clinics of the hospital, and in healthy controls. Recruited to a 4 wk treatment with mastic caps (6 caps / d, 0.37 g / cap) were 10 patients and 8 controls, all of who successfully completed the protocol. Interleukin-6 (IL- necrosis factor-alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), macrophage migration inhibitory factor (MIF) and intracellular antioxidant glutathione (GSH) were evaluated in peripheral blood mononuclear cells (PBMC) before and after treatment. RESULTS: Treating CD patients with mastic resulted in reduction of TNF-α secretion (2.1 ± 0.9 ng / mL vs. 0.5 ± 0.4 ng / mL, P = 0.028). MIF release was signif icantly increased (1.2 ± 0.4 ng / mL vs 2.5 ± 0.7 ng / mL, P = 0.026) meaning that ra ndom migration and chemotaxis of monocytes / macrophages was inhibited. No signifi cant changes were observed in IL-6, MCP-1 and GSH concentrations. CONCLUSION: This study shows that mastic acts as an immunomodulator on PBMC, acting as a TNF-α inhibitor and a MIF stimulator. Although further double-blind, placebo-controlled studies in a large number of patients is required to clarify the role of this natural product, this f inding provides strong evidence that mastic might be an important regulator of immunity in CD.