9 2 00 PER CENT HISTAMINE RELEASE 0 anti-IgE MTNV Normal Control .001 .01 0.1 1.0 10 100 µg/ml STIMULUS FIG. 1. Histamine release from the patient's basophils by MTNV () and anti-IgE antibody (▲). Normal control cells (■) did not respond to any concentration of MTNV. 100- 80- MTNV Pts. Plasma 60 PER CENT HISTAMINE RELEASE 40. T 20- MTNV Normal AB Serum Pts.Plasma a56°C 0.1 1.0 10 100 μg/ml STIMULUS FIG. 2. Histamine release to MTNV after passive sensiti- zation of normal basophils with the patient's plasma (•). No release occurred after sensitization with normal serum () or with the patient's plasma that had been heated to 56° C for 4 hr (0).