Living too close to overhead power lines appears to increase the risk of childhood leukaemia, researchers say.
A major study found children who had lived within 200m of high voltage lines at birth had a 70% higher risk of leukaemia than those 600m or more away.
But the Oxford University team stressed that there are no accepted biological reasons for the results and that they may, therefore, be chance.
Alternatively, it may be down to the environments where pylons are located.
And they said it did not resolve the debate about whether it was unsafe to live next to power lines.
Around 1% of homes in the UK are estimated to be within 200m of high voltage National Grid power lines.
The researchers said their findings showed living in such close proximity to power lines at birth could account for five extra cases of childhood leukaemia in a total of around 400 that occur in a year – a total of 1%.
The British Medical Journal study did not look at level of exposure to magnetic fields.
But other scientists who have considered the issue have suggested that low frequency magnetic fields, such as those caused by the production of electricity, could possibly be linked to cancer.
However, others have disputed this link. And experts agree that there are likely to be many factors involved in leukaemia, including genes and the environment.
Even if the apparent risk was found to be real, the number of cases of leukaemia that would result would be very few, said the authors.