We investigated the effect of rocuronium- and sugammadex-induced mast cell increase and degranulation in rat portal triads. Forty-two rats, in six groups, received either rocuronium 1 mg.kg-1; sugammadex 15 mg.kg-1; sugammadex 100 mg.kg-1; rocuronium 1 mg.kg-1 and 5 min later, sugammadex 15 mg.kg-1; rocuronium 1 mg.kg-1 and 5 min later, sugammadex 100 mg.kg-1; or isotonic saline. Total mast cell numbers were significantly higher with rocuronium only, than in all other groups (p < 0.003), although in all active groups, the number was greater than the control. Total mast cell number was significantly higher with rocuronium and low-dose sugammadex compared with low-dose sugammadex only. The number of tryptase-positive mast cells with rocuronium only was significantly higher than in all other groups (p < 0.003). Tryptase-positive mast cell numbers in both groups receiving both rocuronium and sugammadex were significantly higher compared with both groups receiving sugammadex only. Rocuronium increased mast cell numbers, and degranulation was mitigated by sugammadex. These results suggest that sugammadex may be beneficial in treatment of rocuronium-induced anaphylaxis.