AbstractThe effect of interferon—γ (IFN‐γ) on dengue virus multiplication in human peripheral blood mono‐cytes was investigated. Enriched monocytes were treated with IFN‐γ and then infected with dengue virus type 2 either directly or in the presence of optimal infection‐enhancing levels of antibodies. Pretreatment of monocytes from dengue‐immune donors with 100 IU/ml of IFN‐γ caused 12‐ to 97‐fold and 13‐ to 137‐fold reduction of virus yields at 24 hr after infection in the absence and presence of an anti‐flavivirus monoclonal antibody, respectively. IFN‐γ also diminished virus yields when infection of monocytes from a donor who lacked anti‐dengue antibody was enhanced 40‐fold. The percentage of infected monocytes in IFN‐γ‐pretreated cultures was similarly reduced. Dominance of the antiviral effect of IFN‐γ in monocytes is in contrast to an augmenting effect previously observed in the promonocy