Analysis of baseline population characteristics in a large-scale (N = 1,328), controlled trial of general practitioner intervention against smoking (including advice and advice plus nicotine gum groups) revealed significant associations between the probability of abstinence at 4 months and sex, longest previous abstinence, dependence, motivation to quit smoking, and cigarette consumption. Women did less well overall, and dependence had a greater negative relationship to outcome among women than among men. The positive association of motivation was greater for higher levels of cigarette consumption. In the nicotine gum group, the negative dependence relationship was smaller than that in the other two groups (advice and control). Longest previous abstinence had a curvilinear relationship to outcome, the positive association diminishing as length of abstinence increased. Notwithstanding the above interactions, the gum offer was universally beneficial, except at the lowest levels of dependence, where it had little effect.