This is a study were subjects were randomized to use 3 different concentration of e-nicotine liquid. The subject were confined to a clinical after using the product at home for 2 weeks. This 2-week period allowed subjects to become familiar with the e-cigarette. After two weeks, the subjects were confined to the clinical for one day. They were required to not use any e-cigarettes for 12 hours prior to the visit. Subjects had to have CO level below a pre-specified level, to attend the visit. IF the level, was too high, the visit ws re-scheduled. Subjects were instructed to take 10 puffs on the e-cigarette. Puff topography was measured using the same device for all subjects.