The unfolded protein response (UPR) is a set of pathways activated by the accumulation of improperly folded proteins. It can be triggered by a broad range of stressful conditions which disrupt successful maturation of proteins in the endoplasmic reticulum (ER) by interfering with proper folding, assembly, and posttranslational modification. Recent studies have demonstrated the induction of ER stress and activation of elements of the UPR in human lung cells exposed to diesel exhaust particles, airborne particulate matter, and tobacco smoke. ER stress has been found to play a role in a variety of lung maladies, including cancer, infections, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease. Lung cancer is one of the few diseases where the etiological agent, cigarette smoke (CS), is well known. It is, therefore, desirable to measure dysregulation of the UPR pathway in samples representing both the earliest events (cells exposed to CS in vitro) and in clinical samples from healthy smokers and individuals with smoking-related lung diseases. We hereby provide a detailed description of methods for assessing the degree and timing of cellular response to CS with respect to the three major UPR pathways.