Twenty-five years ago, cigarette smokers in the United Kingdom smoked plain cigarettes with an average tar yield of probably about 35 mg. Now smokers predominantly smoke filter cigarettes and average tar yields have been reduced by half. Epidemiological evidence comparing mortality in smokers of differing types of cigarettes is reviewed. Compared with smokers of higher tar plain cigarettes, smokers of lower tar filters cigarettes have a reduced mortality for lung cancer, for cancer of the buccal cavity, pharynx, larynx, oesophagus, and bladder, for chronic bronchitis and emphysema, and for cirrhosis of the liver. They also have a slightly significant. Problems of interpretation and limitations of the available evidence are discussed. No worthwhile evidence is yet available on smokers of "low tar' (0-10 mg) cigarettes and data are sparse on lifetime smokers of filter cigarettes. Continuing research is important to understand the situation fully, but the trends of lower mortality to be associated with lower tar and nicotine levels are promising.