Perfluorocarbons (PFC) reduce the production of various inflammatory cytokines, including TNF-α. The anti-inflammatory effect is not entirely understood. If anti-inflammatory properties are caused by a mechanical barrier, PFC in the alveoli should have no effect on the inflammatory response to intravenous LPS administration. To test that hypothesis, rats (n = 31) were administered LPS intravenously and were either spontaneously breathing (Spont), conventionally ventilated (CMV), or receiving partial liquid ventilation (PLV). Serum concentration of TNF-α was measured. The pulmonary expressions of TNF-α and TNF-α receptor 1 protein and of TNF-α and ICAM-1 mRNA were determined. LPS caused a significant (P < 0.001) increase in serum TNF-α. Serum TNF-α concentration was similar in LPS/Spont (525 ± 180 pg/ml) and LPS/CMV (504 ± 154 pg/ml) but was significantly (P < 0.001) lower in animals of the LPS/PLV group (274 ± 101 pg/ml). Immunohistochemical data on TNF-α protein expression showed a LPS-induced increase in TNF-α and TNF-α receptor 1 expression that was diminished by partial liquid ventilation. PCR measurements revealed a lower expression of TNF-α and ICAM-1 mRNA in LPS/PLV than in LPS/CMV or LPS/Spont animals. Semiquantitative histological evaluation revealed only minor alveolar inflammation with no significant differences between the groups. Low serum TNF-α concentration in PFC-treated animals is most likely explained by a decreased production of TNF-α in the lung.