Cytochrome P450 1A2 (CYP1A2, EC 22.214.171.124) is a member of the cytochrome P450 monooxidase (CYP) family of microsomal xenobiotic metabolism enzymes. CYPs are membranebound hemeproteins responsible for Phase I biotransformation reactions, in which lipophilic drugs and other xenobiotic compounds are converted to more hydrophilic products to facilitate excretion from the body. CYP1A2 is primarily expressed in liver, intestinal and olfactory mucosal tissue and catalyzes oxidation of polyaromatic and heterocyclic molecules such as aromatic amines. CYP1A2 is responsible for metabolism of approximately 10% of all small molecule drugs commonly used by humans. Polymorphisms in the human CYP1A2 gene have been implicated in clinical drug/drug interactions involving widely-used drugs, including caffeine, theophylline and the antipsychotic clozapine. Isoforms of the CYP1A subfamily are also involved in metabolic activation of environmental pro-carcinogens present in cigarette smoke and combustion exhaust fumes. The PromoKine CYP1A2 Activity Assay Kit enables rapid measurement of native or recombinant CYP1A2 activity in biological samples such as liver microsomes. The assay utilizes a nonfluorescent CYP1A2 substrate that is converted into a highly fluorescent metabolite detected in the visible range (Ex/Em = 406/468 nm), ensuring a high signal-to-background ratio with little interference by autofluorescence. A selective CYP1A2 inhibitor is provided for determination of CYP1A2 activity in heterogeneous biological samples, where other CYP isozymes may contribute to substrate metabolism. The inhibitor displays greater than 20-fold selectivity for CYP1A2 over other CYPs, ensuring targeted inhibition. CYP1A2 specific activity is calculated by running parallel reactions in the presence and absence of the selective inhibitor and subtracting any residual activity detected with the inhibitor present. The kit contains a complete set of reagents sufficient for performing 50 sets of paired reactions (in the presence and absence of inhibitor).