We have performed for the first time a comprehensive profiling of changes in protein expression of soluble proteins in livers from mice treated with the mouse liver tumorigen, propiconazole, to uncover the pathways and networks altered by this fungicide. Utilizing two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS), we identified 62 proteins that were altered. Several of these protein changes detected by 2-DE/MS were verified by Western blot analyses. These differentially expressed proteins were mapped using Ingenuity Pathway Analyses (IPA) canonical pathways and IPA tox lists. Forty-four pathways/lists were identified. IPA was also used to create networks of interacting protein clusters. The protein-generated IPA canonical pathways and IPA tox lists were compared to those pathways and lists previously generated from genomic analyses from livers of mice treated with propiconazole under the same experimental conditions. There was a significant overlap in the specific pathways and lists generated from the proteomic and the genomic data with 27 pathways common to both proteomic and genomic analyses. However, there were also 17 pathways/lists identified only by proteomics analysis and 21 pathways/lists only identified by genomic analysis. The protein network analysis produced interacting subnetworks centered around hepatocyte nuclear factor 4 alpha (HNF4 alpha), MYC, proteasome subunit type 4 alpha, and glutathione S-transferase (GST). The HNF4 alpha network hub was also identified by genomic analysis. Five GST isoforms were identified by proteomic analysis and GSTs were present in 10 of the 44 protein-based pathways/lists. Hepatic GST activities were compared between mice treated with propiconazole and 2 additional conazoles and higher GST activities were found to be associated with the tumorigenic conazoles. Overall, this comparative proteomic and genomic study has revealed a series of alterations in livers induced by propiconazole: nuclear receptor activation, metabolism of xenobiotics, metabolism of biochemical intermediates, biosynthesis of biochemical intermediates, and oxidative stress in mouse liver. The present study provides novel insights into toxic mechanisms and/or modes of action of propiconazole which are required for human health risk assessment of this environmental chemical.