The lung represents an important target for the toxic effects of chemicals. Many of the chemicals require enzymatic activation to exert their adverse effects, which is mostly catalysed by Cytochrome P450 (CYP) enzymes. Although there is considerable evidence that individual members of the xenobiotic-metabolizing P450 family are expressed in human lung tissue at the mRNA level, there is conflicting evidence concerning the following issues: (I) the qualitative expression pattern of CYP isoenzymes; (II) CYP expression at the protein and/or activity level; and (III) interindividual variability of CYP enzymes in human lung. The latter can be the basis for individual susceptibility towards the adverse effects of lung toxicants. In preparing for studying factors to explain interindividual variability of CYP expression in lung tissue, we investigated the qualitative pulmonary expression pattern of xenobiotic-metabolizing CYP enzymes and elaborated the optimal conditions for quantification at the protein and activity level. By using either individual human lung samples or pooled microsomes from different individuals, immunoreactive bands specific for the following CYP enzymes could be determined by Western blotting: CYP1A1, CYP1A2, CYP2E1 and CYP3A5. Western blotting experiments were also supportive of the presence of CYP2A, CYP2B6, CYP2D6 and CYP3A4 in human lung. By using antibodies specific for CYP2C enzymes and CYP1B1, respectively, immunoreactive bands, which differed slightly in mobility from corresponding standards, were detectable. In addition, we measured methoxy- and ethoxyresorufin dealkylase activities and chlorzoxazone (CLX)-hydroxylase activity in human lung and confirmed the specifities of the latter two activities by inhibition experiments. In summary, we have established methodologies to quantify a panel of CYP enzymes in human lung samples among which there are CYP enzymes whose expression at the protein and activity level has not been evidenced so far.