Tumour necrosis factor-alpha (TNF-alpha) and gamma interferon (IFN-gamma) are expressed within human placental villi during normal pregnancy, yet their functions remain unknown. Since villous cytotrophoblasts are within the paracrine reach of this expression, the effects of TNF-alpha and IFN-gamma on a purified population of term placental cytotrophoblasts were examined. After 4 days of culture TNF-alpha alone induced a loss of trophoblast viability as measured by both metabolic capacity (MTT reduction) and DNA content. The combination of TNF-alpha and IFN-gamma enhanced the damaging effect. Neutralizing antibodies against TNF receptor p55, but not p75, partially reversed the TNF-alpha-induced cytotoxicity. After 24 h of culture, TNF-alpha and IFN-gamma increased the fraction trophoblasts containing nicked DNA, and after 60 h, increased the detachment of cells characterized by a distorted morphology, lower DNA content, and fragmented DNA. These results suggest that a physiological role of TNF-alpha and IFN-gamma expression in the placental villi may be to regulate the apoptotic death of villous cytotrophoblasts. The studies also predict potential harmful effects on placental development and function following aberrant inflammatory cytokine expression triggered by intravillous infections.