2) determine whether a second generation device was i) superior for reducing urge to smoke and withdrawal symptoms (WS) and ii) associated with enhanced positive subjective effects. Design:Mixed effects experimental design. Phase 1: reason for e-cigarette choice was assessed via questionnaire. Phase 2: participants were randomly allocated to first or second generation e-cigarette condition. Urge to smoke and WS were measured before, and 10mins after, taking 10 e-cigarette accounted for choice. Only baseline urge to smoke/WS predicted urge to smoke/WS 10 minutes after use (B=0.38; P<0.001 and B=0.53; P<0.001). E-cigarette device was not a significant predictor. Those using the second generation device were more likely to report satisfaction and use in a quit attempt (χ 2 =12.10, P=0.001 and χ 2 =5.53, P=0.02). Conclusions: First and second generation e-cigarettes appear to be similarly effective in reducing urge to smoke and WS during abstinence but second generation devices appear to be more satisfying to users.2