two control monkeys, EHD (untreated and challenged), and a negative monkey (neither treated nor challenged), had very similar background levels of reactivity to the glycoprotein and anti-human antibody as each of the treated monkeys before treatment. A 50-mg/kg dose typically produces serum mAb concentrations in animals on the order of 500 lg/ml after injection [6] . Since the neutralization titer of KZ52 (IC 90 ) for ZEBOV is on the order of 0.5-2.5 lg/ml, depending upon the target cell and the presence of complement, the concentrations of KZ52 in the animals at the time of challenge and for the first few days were, as expected, greater than, or on the order of 100 3 IC 90 . These concentrations typically provide sterilizing immunity against challenge by a number of viruses [4, 20] .