A panel of 11 murine monoclonal antibodies directed against dengue type 2 was evaluated for antigen specificity by dot immunobinding assay and Western blot analysis and for in vitro and in vivo biological activities. Nine of the 11 monoclonal antibodies reacted with viral E-glycoprotein based on the Western blot analysis; one reacted with a 36 Kd protein present in dengue-infected C6/36 mosquito cells. The nine E-glycoprotein-reactive monoclonal antibodies also neutralized dengue 2 virus in a plaque reduction assay. Of the neutralizing monoclonal antibodies, five passively protected mice in vivo against lethal intracerebral dengue 2 challenge. The protective monoclonal antibodies were directed against viral determinants that fell into at least three spatially separate families of epitopes on E-glycoprotein, the antigenicities of which were preserved after heat/detergent denaturation.