Scientists will today warn mobile-phone users to consider using low-emission or hands-free devices following research that links use with brain tumours.
Findings from two new studies could be a problem, the scientists claim, and call for the public to be given full health information on the use of mobiles.
A Swedish cancer specialist, Dr Lennart Hardell, author of one of the new studies, tells BBC's Panorama programme there is a biological indication of a problem that needs further study.
"I think that until we have the definite conclusion, the definitive results of much larger studies, we need to minimise exposure to human beings," he tells the programme, to be screened tonight on BBC1 at 10 p.m.
His study looked at brain tumour sufferers and found a correlation between phone use and cancer.
He found that for those using their mobile on the right side of their head, the risk of getting a tumour increased by almost 2 1/2 times and for those who used it on the left side it increased by almost 2 1/2 times as well.
In the US Dr George Carlo, head of the $25 million research body funded by the mobile phone industry, speaks out for the first time about a new and as yet unpublished US study that also shows an increased risk of getting a type of rare brain tumour.
He says that taking into account the two new studies, it is no longer a responsible position for the manufacturers to say there is no problem.
"We clearly have results that suggest there could be something more here than meets the eye.
"The science we have today clearly shows that this is not black and white, that we have moved now into a grey area that suggests there could be a problem that needs to be looked at very, very carefully. That grey area needs to be acknowledged," he adds.
The programme also speaks to people who claim they have been made ill by mobile phones.
Mr Steve Corney, who was a BT engineer four years ago, using a new digital phone for up to five hours at a time, tells the programme he is now out of work and suffers memory loss and speech problems.
Research carried out exclusively for Panorama by Britain's National Physical Laboratory also features in the programme.
The study looked at the levels of emissions absorbed by the brain from different makes of mobile phone.
The research shows that although all seven of the phones tested were below the safety limit of 10 specific absorption rates, SARs, set by the national Radiological Protection Unit, there was a considerable difference between the lowest and the highest.