Recombinant cytochrome P450, isozyme 2C9, (CYP2C9) may be used in toxicity and drug metabolism/ pharmacokinetics research to identify its specificity and activity versus xenobiotic and endogenous compounds. Recombinant cytochrome P450, isozyme 2C9, may be used separately or as a component of a P450 isozyme panel to identify and characterize natural and synthetic selective inhibitors that affect the metabolism of toxic compounds or therapeutic drugs such as warfarin, bosentan, and fluoxetine.