E-vapor products (EVPs) are becoming an accepted alternative to conventional cigarettes among smokers. Despite the increasing popularity of EVPs, little information exists on the fate of the main ingredients glycerol (G), propylene glycol (PG) and nicotine (Nic). Since exposure to G and PG can occur from other sources, stable-isotope labelled e-liquid ingredients can directly assess exposure. Accordingly, we developed and applied methods that allow the unequivocal determination of EVP use-related uptake of e-liquids containing stable isotope-labeled Nic, G and PG. This approach assesses biomarkers to measure the absorption, metabolism and further fate of PG, G, and Nic as well as compounds formed from these precursors in the vapor, or formed endogenously. A diet-controlled clinical study was conducted with 25 healthy male subjects. The subjects were divided into 3 groups: Group I (N = 10): experienced EVP users, vaping under low wattage conditions; Group II (N = 10): experienced EVP users, vaping under high wattage conditions; Group III (N = 5): smokers, smoking conventional non-filter cigarettes spiked with stable isotope-labelled Nic, G and PG (positive control). The study was divided into two settings: confinement (Part A) and ambulatory (Part B). Periodic samples of various biofluids (plasma, urine, saliva and sputum) were collected. The presentation will include the detailed study design. To the best of our knowledge, this is the first study dealing with the absorption, metabolism and formation of degradation products in the human body solely derived from the consumption of EVPs. These data are important for providing foundational knowledge regarding EVPs.