Trifluoroacetylated (TFA)-protein adducts were investigated by immunoblotting in liver and plasma of guinea pigs treated with the hepatotoxic anaesthetic halothane or the chlorofluorocarbon replacement 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123). Male outbred Hartley guinea pigs (320-400 g) were administered HCFC-123 (1, 5, 10 and 15 mmol/kg b.w.) or halothane (positive control, 10 mmol/kg b.w.) i.p. in corn oil. Blood and liver samples were collected 24 h after administration of HCFC-123 or halothane. Immunoreactive bands were demonstrated in liver microsomes at all HCFC-123 and halothane concentrations, and in plasma of animals treated with 10 and 15 mmol/kg b.w. HCFC-123 and 10 mmol/kg b.w. halothane, while no alteration of microsomal P450 content or monooxygenase activities markers of the P450 2A, 2E1 and 2B isoforms was observed. Instead, when HCFC-123 was administered at doses of 1 and 5 mmol/kg b.w., the 2E1-dependent p-nitrophenol hydroxylase activity was enhanced. The presence of TFA-proteins in plasma was always associated with hepatic damage. However, mild liver damage in some animals treated with 1 or 5 mmol/kg b.w. HCFC-123 was not associated with the presence of TFA-proteins in plasma. This indicates a lower threshold dose for the appearance of TFA-proteins or damage in the liver (1 mmol/kg b.w.) than for the presence of TFA-proteins in plasma (10 mmol/kg b.w.), thus suggesting that the presence of TFA-proteins in plasma may be the result of liver damage.