We have previously reported that halothane's reactive oxidative metabolite, trifluoroacetyl halide (CF3COX), forms trifluoroacetylated (TFA) covalent adducts within and on the outer surface of hepatocytes, when halothane is administered to rats or humans. It was additionally found that certain individuals, who have had halothane-induced hepatotoxicity, possesses anti-TFA antibodies in their sera. This finding suggested that the toxicity may have been initiated by a sensitization against TFA cellular proteins. In order to investigate this idea, we began elucidating the identify of the TFA adducts. Last year we reported that the major TFA adduct within the cells of phenobarbital treated rats that were administered halothane was identified as a 54 kD form of microsomal cytochrome P-450. We have now developed a general immunoaffinity purification procedure for isolating TFA proteins and have applied it to purify the TFA proteins found in the liver microsomal fraction of normal rats treated with halothane. One major (Mr 59,000) and two minor (Mr 76,000 and 92,000) TFA protein fractions were isolated by this method. Preliminary studies suggest that the 59 kD protein maybe a form(s) of cytochrome P-450 that has not been previously identified. The physiological function of this enzyme as well as the potential role of all three TFA proteins as immunogens in halothane-induced hepatotoxicity is currently being investigated.