Most occupational exposures to toxic chemicals occur in the context of complex mixtures, often in combination with varied diet, prescription drug use and disease. In principle, information-rich metabolic analyses provide an approach to study toxicologic consequences of such complex chemical interactions by revealing metabolic perturbations before irreversible injury occurs. This pilot study tests the feasibility of using GSH redox state and high resolution proton NMR spectroscopy (1H-NMR) to detect metabolic changes due to chemical interactions. The proposed model involves interaction of chemical exposure (2 doses of acetaminophen, APAP, 15 mg/kg) and 2 days of sulfur amino acid- (SAA-) free diet. 30% of APAP metabolism occurs through pathways dependent upon SAA metabolites and up to 50% of the RDA for SAA is needed to metabolize 2 doses of APAP. Both treatments are without toxicity in humans and both affect GSH homeostasis, which will be assessed in vivo by plasma measurements. Inter-individual variation will be minimized with each individual being his/her own control. Environmental and dietary influences will be controlled in a clinical research unit. Aim 1 is to determine whether SAA-free diet and APAP independently perturb GSH redox homeostasis. Aim 2 is to determine whether APAP intake interacts with SAA-free diet in affecting GSH redox state. Aim 3 is to use 1H-NMR spectroscopy to determine whether exposure to APAP and SAA-free diet interact in their effects on metabolic profile. The results will provide key data on the suitability and sensitivity of redox measurements and 1H-NMR spectroscopy for study of chemical interactions. This could provide a foundation for the use of perturbation of metabolic profile as a means to identify risks and consequences of complex chemical mixtures which would be especially relevant to occupational exposures in combination with therapeutic drugs and other health risk factors.