Hepatic metabolism of halothane, methoxyflurane, cyclopropane, Ēthrane, and Forane was studied in miniature swine, using a modification of a technique which demonstrated that the liver extracts (metabolizes) a greater fraction of halothane from hepatic blood flow at lower than at higher anesthetic partial pressures. Animals were exposed to constant, low subanesthetic concentrations of each anesthetic for periods of 20 hours to one week and measurements of extraction made thereafter. We found considerable hepatic metabolism of halothane and methoxyfiurane, little or none of Ēthrane, and none of cyclopropane or Forane. These results may be related to toxicity since toxic effects of inhalation anesthetics may be due to their metabolites.