Organisms are constantly exposed to an ever changing spectrum of foreign chemicals or xenobiotics . By virtue of that, organisms evolved generic degradation mechanisms as for example phase I and phase II metabolism reactions. Cytochrome P450 (CYPs) enzymes are typically involved within the phase I metabolism. The expression of several ytochrome P450 enzymes can be induced by the intake of xenobiotics as for example fungicides. Hence, the aim of this project was to develop a mass spectrometry-based immunoassay to quantify CYPs in mouse liver samples. For the development, several parameters were investigated. The detection compatibility of the preselected peptides that should represent the CYPs as well as the digestion kinetics, the accuracy and the linearity were determined. In addition, the antibody-protein ratio used in the enrichment step and the chromatographic separation were optimized. Out of all 45 peptides, that represent 39 CYPs, passed 15 peptides all stages of the development process. The ideal digestion duration was determined to be 16 h and the linearity showed excellent results. With these 15 peptides, representing 13 CYPs, cyproconazole- or prochloraz-treated wild type and transgenic hCAR/hPXR mice were analyzed. The measurement revealed that these fungicides induced the expression of every analyte except for Cyp2e1. Furthermore, the WT-mice reacted more sensitive towards the fungicides. This suggests higher affinities of the fungicides to the murine receptors than to the human receptors.