ABSTRACT-Assessment of mouse paw edema induced by the passive allergic reac tion was made by the previously reported dye-leakage method. The edema was in duced by the injection of antiserum against ovalbumin into the paw, followed by the intravenous injection of ovalbumin 10 min before or 72 hr later. The latter reaction may be mainly mediated by heat-labile IgE. Both of the edemas were suppressed by pretreatment with mepyramine, methysergide, PAF-antagonists, or dexamethasone, and the latter suppressed by the lipoxygenase inhibitor AA-861, suggesting that hista mine, serotonin, PAF, and leukotrienes are involved in exudate formation in these edemas.Vascular permeability increase is a phe nomenon seen in the initial phase of acute in flammation and allergy; and assessment of the reaction was previously made in the skin, paws or pleural cavity of various experimental animals by the use of pontamine sky blue dye exudation (1-3). As mouse dorsal skin is too thin for injection, we developed a paw edema model to assess the vascular permeability in crease in the mouse (4).In the present work, we applied the method to study the allergic exudation in the mouse paw in which the passive subcutaneous anaphylactic reaction had been induced (5).Male 5-week-old ICR mice (Shizuoka Laboratory Animal Center, Hamamatsu) were used for the induction of inflammation.Female 5 8-week-old Balb/c mice were used for antiserum production; i.e., they were in traperitoneally injected with 50 pg of ovalbu min and 15 mg of alum and then boostered with 5,ug ovalbumin on the 10th day. Anti sera were obtained on the 17th day.Two models were devised for the passive anaphylaxis reaction in the mouse paw. [1] 10 min anaphylaxis: ICR mice were anesthetized with pentobarbital sodium (50 mg/kg), and ovalbumin (4 mg/kg) and pontamine sky blue (PSB, 60 mg/kg) were injected into a tail vein; and then 10 min later, antiserum to oval bumin was injected into the foot pad (50,ul vehicle was injected into the other foot). Sixty minutes later, the mice were exsanguinated, and both feet were removed.[2] 72-hr anaphyl axis: ICR mice were injected with 50,ul of va rious dilutions of antiserum into the paw under light ether anesthesia (50 ,ul of vehicle was injected into the other foot); and 72 hr later, the mice were anesthetized with pento barbital sodium (50 mg/kg), and then ovalbu min (4 mg/kg) and PSB (60 mg/kg) were in