PUT a mobile telephone to your ear and your head absorbs electromagnetic microwaves from the antenna as part of the radio transmission that makes the phone function. The question now being investigated by research scientists is whether this radiation can damage your health.

Some scientists are sufficiently worried about the effects to recommend modified use of mobile handsets. A few even advise not using them at all. Most are more sanguine, insisting that no research to date suggests serious cause for concern.

But all agree that research has fallen well behind the explosive growth in the use of mobile telephones worldwide, with subscriber numbers increasing at a rate of 50 per cent a year, reaching 85 million worldwide in 1995.

There is a consensus which includes the mobile manufacturers and operators - that more research is required before a definitive answer can be given on whether using mobile phones threatens to cause or exacerbate a range of conditions from brain cancer, through asthma, to headaches and nausea.

Research to date has already established one possibly dangerous effect of mobile phones: digital handsets have been shown to interfere in some circumstances with heart pricemakers, prompting a warning to users from US and Canadian health authorities.

But the picture is less clear when it comes to the biggest fear - that of possible links to cancer or other serious conditions such as Alzheimer's disease. Last year, a US court threw out a lawsuit by a man who claimed his wife had died of a brain tumour caused by using a mobile telephone, saying there was no scientific evidence to support his allegation.

Last month, concerns about mobile telephone growth prompted the WHO to launch a 53.3 million (£2.1 million) five year project to study the possible health effects of all electric and magnetic fields from a range of devices, including microwave ovens and electric razors, as well as mobile phones.

The European Commission has set up a 10 strong panel of experts to review the research done so far worldwide and to recommend further areas of investigation.

The chief source of concern about mobile phones is the radio transmitter - the device's most vital component. Mobile phones work by using radio waves to link to radio base stations. The base stations in turn are linked to the switching stations which together make up a mobile network.

The radio in a mobile handset emits electromagnetic signals, or microwaves, similar to those in a microwave oven. Although many modern electronic devices emit such radiation in varying strengths, few are held as close to the brain as a mobile phone. This has led to some alarmist headlines about mobile phones "cooking" the brain.

In fact, the power levels used in a mobile phone, at around 1 watt or less, are tiny compared with a microwave oven operating at 600 watt or more and not all the power is absorbed by the head when making a call.

Police and military around the world have used hand held radio sets - often more powerful than modern mobile phones for years. The output levels of mobile handsets are already operating within standards set by national and international authorities.

The operators and manufacturers say there is no cause to suspect that mobile phones pose a danger.

The manufacturers may in any case produce a solution. They are striving to reduce the power output of mobile phones in order to increase the time they can be used without having to change or recharge the battery. Latest digital phone systems are also using higher radio frequencies, which do not penetrate the body as much. Users worried about possible ill effects can already buy an earpiece and microphone.

In the meantime, one observer draws a wry conclusion: "I think you are most likely to be injured from mobile phone use by crashing your car while talking and driving at the same time. But from a world health perspective we have to look into these other issues further."