In 1981 an influential Japanese study showed an association between passive smoking and lung cancer. This article documents the tobacco industry's attempts to refute this study by producing a credible alternative study

In 1981 Japanese investigator Takeshi Hirayama published a cohort study examining the association of passive smoking and lung cancer among non-smoking wives of smokers in Japan.1 The study concluded that wives of heavy smokers had up to twice the risk of developing lung cancer as wives of non-smokers and that the risk was dose related. The Hirayama study was influential because it launched an extraordinary amount of critical debate 2 3 and has been one of the most frequently cited studies in regulatory proceedings, 4 5 risk assessments,6 and the media.7

The tobacco industry has used a variety of tactics to maintain scientific debate about whether secondhand smoke has any harmful effects. 5 6 8^–14 We identify and analyse internal tobacco industry documents that describe the industry's response to the Hirayama study.