Aims. To explore whether the introduction onto cigarette packs of new larger, more prominent health warnings in black on white would lead to an increase in: noticing warnings, thoughts about the effects of smoking, and consequent behaviours of not smoking a planned cigarette and/or prematurely stubbing out one already lit. In addition evidence was sought linking these effect to smoking cessation. Design. Two national cross-sectional surveys of broadly representative samples of smokers: one about 2 weeks before the mandated introduction date of the warnings, and a follow-up 6 months later, pan-way through implementation. A longitudinal subsample of smokers from the initial baseline survey was resurveyed at follow-up. Setting. In Australia, new health warnings and strengthened contents labelling of cigarette packets were mandated for cigarettes manufactured from 1 January 1995. Participants. Broadly representative samples of Australian smokers: 510 at baseline, and 512 at follow-up. Two hundred and forty-three of the baseline sample were also resurveyed. Measurements. Self-report on effects of warnings and smoking cessation activity. Findings. In the cross-sectional sample at follow-Up, 66% of smokers reported at least sometimes noticing the health warnings when taking out a cigarette (compared with 37% at baseline), and 14% reported they had refrained from smoking on at least one occasion as a result (compared with 7% at baseline). Not smoking as a result of noticing the (old) warnings at baseline was predictive of quitting at follow-up. Frequency of stubbing out cigarettes before they were finished as a result of thinking about smoking-related harm was not affected by the new warnings, but was predictive of making quit attempts. Conclusions. The new health warnings were more potent at stimulating both thoughts about negative effects of smoking and the appropriate consequent action of not smoking the planned cigarette. This is important as spontaneous rejection of cigarettes predicted subsequent cessation.