Scientists say they have found a new way to predict lung cancer - by looking at a person's toenail clippings.
Experts at the University of San Diego in California have found that measuring nicotine levels in clippings can give a fairly accurate idea of future risk.
Slow-growing toenails provide a barometer of chronic smoke exposure the American Journal of Epidemiology says.
Men with the highest readings were over three times as likely to get lung cancer as those with the lowest.
Toenails not only spot which smokers are most at risk but also which non-smokers are as well.
The researchers studied more than 800 men, some with lung cancer and some without.
Toenail nicotine levels were found to be a strong predictor of lung cancer.
Some of the men with the highest levels of nicotine were non-smokers who, presumably, had been exposed via passive smoking.
Lung cancer is the most common cancer in the world with 1.61 million new cases diagnosed every year.
The vast majority of lung cancers are caused by cigarette smoking.
The lifetime risk of developing lung cancer is thought to be 1 in 14 for men and 1 in 19 for women in the UK.
About 41,000 people were diagnosed with lung cancer in the UK in 2008, which equates to 112 people every day.