UK research has cast further doubt on claims of a link between overhead power lines and childhood leukaemia.
Some scientists say strong magnetic fields in homes near high-voltage cables may increase the risk of cancer.
Scientists are divided over the risks of living under power lines
They believe electromagnetic fields from power lines or household appliances may impair the body's ability to fight disease.
But the theory has been dismissed by researchers at the National Radiological Protection Board (NRPB) in Oxfordshire.
They say they have failed to find evidence to support it in laboratory experiments.
"Some studies in the past have thrown up evidence of a weak link between unusually strong magnetic fields experienced in some homes, and leukaemia in children," said lead researcher Dr David Lloyd.
"We tried to produce this effect in cells in the lab, but couldn't find it even using magnetic fields stronger than people would experience in everyday life."
Large-scale studies looking at disease trends have found that there is no link between magnetic fields given off by overhead power lines or electrical appliances and most cases of childhood leukaemia.
"Studies show very clearly that the vast majority of children in the UK are not exposed to levels of electromagnetic radiation that would constitute any risk at all," said Dr Lesley Walker, of Cancer Research UK.
However, the NRPB, the UK Government's radiation watchdog, has admitted in the past that there is a "weak association" between electromagnetic fields and increased risk of childhood leukaemia.
In homes with prolonged exposure to unusually strong magnetic fields - 0.5% of those in the UK - there may be a slight increased risk of the disease. Researchers have been unable to explain why this might be the case.
"Studies like ours have failed to uncover a pathway by which magnetic fields could cause childhood leukaemia - and it's looking probable that none exists," said Dr Lloyd.
This position is disputed by some scientists, including Professor Denis Henshaw of Bristol University.
He questions the conclusions of the latest study, published in the British Journal of Cancer.
"Country studies have not had enough statistical power to see an increase of childhood leukaemia near power lines," he told BBC News Online.
"The pooled analysis of country studies has clearly shown a doubling of child leukaemia at levels well below what you get under power lines."
He believes melatonin plays a role in protecting the body against damage that can lead to leukaemia and may be disrupted by strong magnetic fields.
"The study carried out by Dr Lloyd and colleagues did not involve melatonin," said Professor Henshaw. "Therefore, while publication of this study is to be welcomed, failure to observe an effect of magnetic fields on these cells may be unsurprising."
The latest study used blood cells from a donor to test the effect of magnetic fields on the normal repair process.
The researchers blasted cells with radiation to create the sort of damage that leads to cancer.
They found that the cells repaired themselves naturally, even if they were exposed to stronger magnetic fields than those found in British homes.