Fig. 3. Inhibition tests using the quaternary ammonium morphine–IgE test. Sera from five neuromuscular blocking agent (NMBA) skin test–positive reactors were incubated volume for volume with the administered NMBA(s) in serial dilution and pure solution or with buffer. Percent response: (response of serum with inhibitor)/(response of serum with buffer), after subtracting the system background response (buffer alone).