A tool for predicting the risk of clinical depression in teenage boys has been developed by researchers.
Looking for high levels of the stress hormone cortisol and reports of feeling miserable, lonely or unloved could find those at greatest risk.
Researchers at the University of Cambridge want to develop a way of screening for depression in the same way as heart problems can be predicted.
However, their method was far less useful in girls.
Teenage years and early adulthood are a critical time for mental health - 75% of disorders develop before the age of 24.
But there is no way to accurately say who will or will not develop depression.
Now researchers say they have taken the "first step" towards a screening tool.
Tests on 1,858 teenagers, reported in Proceedings of the National Academy of Sciences, combined hormone levels and mood questionnaires to assess risk.
They showed that having both high cortisol levels and depressive mood symptoms posed a higher risk of depression than either factor alone and presented a risk of clinical depression 14 times that of those with low cortisol and no depressive symptoms.
Around one in six boys was in the high-risk category and half of them were diagnosed with clinical depression during the three years of study.
One of the researchers, Prof Ian Goodyer, said: "Depression is a terrible illness that will affect as many as 10 million people in the UK at some point in their lives.
"Through our research, we now have a very real way of identifying those teenage boys most likely to develop clinical depression.
Women are twice as likely as men to develop depression during their lifetimes, but the test was little help in determining risk.
One theory is that women naturally have higher cortisol levels, which affects their risk.
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Have any of you whether you're male or female been diagnosed with clinical depression?