The actions of retroviral infections, aging, and cocaine and morphine injection on cytokine production were investigated in C57BL/6 female mice. Retroviral infection with LP-BM5 murine leukemia virus was further developed as a model of murine acquired immunodeficiency syndrome (AIDS). The effects of cocaine and morphine on gamma-interferon (IFN) and tumor necrosis factor (TNF) production in vivo and with isolated spleen cells were measured by a sandwich enzyme-linked immunosorbent assay (ELISA) method. Serum IFN was generally not detected in any group except mice injected with saline and young mice infected with LP-BM5 virus. Splenocytes from mice with murine AIDS produced less IFN when stimulated in vitro by ConA. In aged mice, IFN production by spleen cells was severely suppressed by retroviral infection. Cocaine had a tendency to suppress IFN production by stimulated cells in vitro. Morphine tended to reduce IFN production by spleen cells from retrovirally infected animals. The serum TNF level in mice with murine AIDS was elevated creating higher levels in morphine and morphine plus cocaine treated uninfected mice while cocaine injection eliminated serum TNF. When stimulated in vitro by lipopolysaccharides (LPS), splenocytes from mice with murine AIDS also produced more TNF than uninfected controls. TNF production in vitro and in vivo was significantly increased by retroviral infection. Therefore, results indicate that cocaine and retroviral infection modulate TNF and IFN production.