The purpose of this study was to examine the effectiveness of different practice-based approaches to assist patients of primary care physicians to quit smoking and sustain cessation. Forty-four nonsmoking general practitioners volunteered for the study. After a period of training, they randomized 923 smoking clients, unselected for motivation toward quitting, to four different intervention groups: (i) minimal intervention, consisting of one single counselling session and a brief handout on quitting techniques; (ii) repeated counselling including reinforcing sessions at Months 1, 3, 6, and 9; (iii) repeated counselling and use of nicotine gum; and (iv) repeated counselling and spirometry. Biochemically validated smoking status was assessed at six and 12 months after recruitment. The proportion of verified quitters at 12 months was 4.8 percent among subjects randomized to the minimal intervention group, compared to 5.5 percent, 7.5 percent, and 6.5 percent among those randomized to the three repeated-counselling groups. In no treatment group was the outcome significantly different from that for one-time counselling at the (P less than 0.05) level. Lack of power, contamination, and low attendance at reinforcing sessions should be taken into account in interpreting the results.