We described a case of anaphylaxis diagnosed by the evaluation of plasma mast cell tryptase and a case of anaphylactoid reaction. In a patient undergoing pulmonary lobectomy, anaphylaxis, showing the elevation of plasma tryptase, was provoked by physiological glue for hemostasis during the operation. During the operation, cardiovascular collapse occurred suddenly, at which time the cause was not diagnosed. After completion of the operation and removal of drapes, diffuse urticaria with wide erythema on the torso and the upper extremity was noticed. Suspecting allergic adverse reaction, plasma tryptase was measured 2h and 5h after the start of the episode, showing 34.6 ng.ml-1 at 2h and 15.3 at 5h. Because these elevations of plasma tryptase indicated degranulation of mast cells, evaluation of the causative drugs was performed 7 weeks after the episode. Physiological glue was confirmed to be causative drug. In another patient for total hysterectomy and bilateral oophorectomy, adverse reaction occurred after completion of the operation and extubation. Increase in plasma histamine concentration to 4.94 ng.ml-1 that could induce systemic reaction was noticed; however, concentrations of plasma tryptase 25 min, 3h and 7h after the episode were not elevated. This finding indicated that the adverse reaction was not based on degranulation of mast cell, and was anaphylactoid reaction provoked by nonspecific histamine-release. In conclusion, measurement of plasma tryptase is a useful method for differential diagnosis of anaphylaxis and anaphylactoid reaction.