Schizophrenia is a chronic and debilitating psychiatric illness affecting approximately 1% of the world's population for which there is no cure and treatment options are limited. Poor understanding of disease pathology and the difficulty in modeling psychiatric symptoms in animal models has hindered the search for a cure. Despite these difficulties great progress has been made on several fronts. Genetic studies have identified risk genes for disease, while fMRI and histology experiments have located brain regions with altered activity and cytoarchitecture. Pharmacology, molecular and immunology studies have identified receptor signaling pathways that are perturbed as well. One of the biggest challenges currently facing the field is elucidating the mechanisms linking genetic and environmental risk to the altered processes observed in the brains of schizophrenic patients. One approach to this question may be to investigate the postmortem brain tissues of patients. The goal of this thesis is to use mass spectrometry based proteomics to investigate the expression and partitioning of postsynaptic density proteins in these tissues. The postsynaptic density is implicated in disease pathology by genetic, cytoarchitecture and molecular studies. Thus, there is a good possibility that its protein composition reflects the crossroads of genetic risk and dysregulated molecular and developmental processes. A qualitative analysis of the human postsynaptic density was performed to catalog the proteins therein. Data from this experiment was harnessed to develop a mass spectrometry method for the targeted quantification of over 200 synaptic proteins. This method was then used to validate subcellular fractionation of human postmortem brain tissue to capture synaptic microdomains. Finally, this targeted mass spectrometry method was utilized to quantify synaptic protein expression and PSD partitioning in postmortem brain tissues of subjects and patients. The enrichment of PSD proteins was elevated in tissue from schizophrenic subjects compared to controls, while total protein expression was unaltered. This data suggests that partitioning, not expression, of postsynaptic proteins is altered in schizophrenia. The results of this study demonstrate the power of a targeted mass spectrometry approach and provide an important context in which to study the dysregulation of synaptic processes in schizophrenia.