BACKGROUND Reducing tar yields of manufactured cigarettes has been an important plank of government policy on tobacco, but sale weighted yields are not routinely published. METHODS Tar, nicotine, and carbon monoxide yields measured by the Laboratory of the Government Chemist were combined with cigarette brand market shares from national surveys of smoking behaviour to generate sales weighted yield estimates for the period 1972-99. RESULTS Sales weighted mean tar yields have declined steadily and in 1999 were 9.6 mg per cigarette, less than half their level in 1972. Over the same period nicotine yields have come down from 1.33 mg to 0.79 mg per cigarette. Carbon monoxide yields have shown smaller declines. At the same time as absolute yields have declined, there have also been changes in tar to nicotine ratios. Smokers in 1999 were exposed to 22% less tar per unit of nicotine than in 1973, and smokers of low tar brands have consistently been exposed to less tar per unit of nicotine than smokers of other brands. CONCLUSIONS The value of reducing cigarette tar and nicotine yields has been questioned, since the tendency of smokers to compensate for reductions in nicotine delivery undermines the policy. The favourable trends in tar to nicotine ratios suggest that, despite this, there may have been some modest public health benefit. It cannot be assumed that future reductions from present levels would necessarily result in further improvement in tar to nicotine ratios. An explicit focus on the ratio of tar to nicotine may provide a metric of greater relevance for public health than the present emphasis on absolute tar yields.