Murine monoclonal antibodies which recognize similar epitopes as the naturally occurring human IgG anti-IgE antibodies were used to study their role in interfering with the effector functions of IgE. Two types of antibodies were found which were either anaphylactogenic or did not release histamine from human basophils. However, both types of antibodies were capable of inhibiting binding of IgE to FcεRII. Furthermore, the nonanaphylactic antibody was capable of removing IgE from FcεRII+ cells, but no antibodies were found which removed IgE from FcεRI+ cells. Thus, anti-IgE antibodies may interfere with the pathophysiological role of IgE.