Purpose: Parkinson's disease (PD) is the second most prevalent neurodegenerative disease. It is generally diagnosed clinically after the irreversible loss of dopaminergic neurons and no general biomarkers currently exist. To gain insight into the underlying cellular causes of PD we aimed to quantify the proteomic differences between healthy control and PD patient cells. Experimental Design: Sequential Window Acquisition of all THeoretical Mass Spectra was performed on primary cells from healthy controls and PD patients. Results: In total, 1948 proteins were quantified and 228 proteins were significantly differentially expressed in PD patient cells. In PD patient cells, we identified seven significantly increased proteins involved in the unfolded protein response (UPR) and focused on cells with high and low amounts of PDIA6 and HYOU1. We discovered that PD patients with high amounts of PDIA6 and HYOU1 proteins were more sensitive to endoplasmic reticulum stress, in particular to tunicamycin. Data is available via ProteomeXchange with identifier PXD030723. Conclusions and Clinical Relevance: This data from primary patient cells has uncovered a critical role of the UPR in patients with PD and may provide insight to the underlying cellular dysfunctions in these patients.