Three nights a week throughout February and March this year, 19-year-old Julianne O'Keeffe didn't go to bed. At midnight she would cycle four miles through the darkness to Tory Hill outside Waterford in Ireland to join a picket line in a forest. At six o'clock she would cycle home, have an hour's sleep and then go to her job in a bookshop.

To the 600 or so inhabitants of Bigwood, which lies at the foot of Tory Hill, Julianne's dedication is nothing special. Since February, local women and children have maintained a 24-hour picket to challenge workers going to the summit of the hill where a microwave transmission mast is being erected. Dozens of them - farmers, teachers, shopkeepers - have vowed to go to prison rather than give up the fight.

Tory Hill rises 960ft above typical Irish farmland where black-and-white cows with swollen udders browse near brilliant yellow gorse hedgerows. It occupies a special place in the hearts of the locals. 'It is a beautiful, holy place,' says John Ryan, a carpenter. 'Now there is only a cross up there to celebrate the faith of our ancestors. I will not allow it to be desecrated by this monstrosity.' Around him, farmers and their wives nod in agreement. Mr Ryan has made a scale model of the planned mast to show its overpowering height in relation to the nearby cross.

The slender 300ft metal mast, shaped like an isosceles triangle, is planned to be part of a network of 29 that has been under construction across Ireland for the past five years. The masts are to bring foreign television programmes, mainly those from the BBC and ITV, to rural parts of the country that are not covered by the cable systems operating in most of the larger towns.

So are the inhabitants of Bigwood really that averse to Don't Forget Your Toothbrush? The problem, they say, is not with the message or even the medium, but with the way it is transmitted. The masts make up what is known as MMDS - Microwave Multipoint Distribution System - which will bathe the entire country in very low level microwave radiation.

'This is a biological experiment on a massive scale,' says Rick Metcalf, a builder from England who only moved into the area two years ago. 'Several European countries have already rejected this system and no one knows what sort of long-term effects it may have.'

Cablelink, the consortium that is building and operating the Tory Hill mast, claims it is working well within internationally approved safety limits. The Irish telecommunications minister recently remarked that you would have to sit next to the mast for 40 years to receive the same dose that you would get from four minutes inside a microwave oven.

But such reassurances have failed to put many of the inhabitants of Bigwood at ease. 'We run a stud farm,' says Mary Fox. 'What happens if the mares that come to be covered from England start producing deformed foals?'

So the campaign has continued. Victories include persuading the electricity board not to cross the picket line and local contractors to refuse to work there; those that do have demanded a substantial bonus.

There have been failures in the campaign too. Early one morning last month, two men, their faces concealed by balaclavas, attacked a security firm's hut on the top of the hill, forced the two guards to remove their shoes and socks and made them to flee barefoot down the hill before setting fire to the hut and a mechanical digger.

'That was a low point for us,' Mr Metcalf admits. 'None of us was involved in it but the Garda came down heavily on us and we lost a lot of goodwill.' One of the guards subsequently died of a heart attack, but an inquest declared that his experiences that night had not contributed to his death.

To provide their campaign with a scientific grounding, the protesters invited the English bioelectronics consultant Roger Coghill to give his views. Mr Coghill had already advised families in England who have been involved in disputes over the possibly harmful effects of electromagnetic radiation.

'The official safety levels for microwaves were originally set to avoid the dangers of heating, but there is a growing evidence that microwaves can have effects at levels way below those that produce heat,' he told a packed meeting in Waterford last week.

'In the past three years at least 17 studies have produced harmful effects on animals and cells - including cancer and immune system problems - by putting them in very weak microwave fields. And we are talking a few hours or a few days, rather than the 24-hours-a-day, seven-days-a-week that this mast will be operating. One study on humans, just completed in Switzerland, found an effect on people one kilometre away from a radio mast.'

While the health aspect is still controversial, the issue has been given an additional twist by the fact that Bigwood and the villages around are already getting the full range of British television. They get it from the Deflectors, electronic entrepreneurs who pick up the signals from the coast and amplify and rebroadcast them for pounds 60 a year.

''MMDS will put them out of business and charge us pounds 300 for the same service. Who needs it?' says Mr Metcalf.

The fact that the Deflectors are also fighting MMDS has given the protesters an opportunity to make use of television to put their case. Until the Tory Hill picket, the Deflectors only acted as relay stations, but they are technically able to broadcast their own material. Already those watching BBC 2 have on several occasions had scheduled programmes replaced by details of the Tory Hill campaign. Later this week there are plans to broadcast a videotape of Mr Coghill's presentation in the Waterford area. There are rumours that the tape will be shown by deflectors all over the country.

On the one hand, the battle of Tory Hill is a uniquely Irish conflict; no British protest would have quite the same religious dimension. The protesters are concerned about the blighting of an annual Mass held on the hilltop; and one of the guards sitting out a lonely vigil each night declared he was only doing it to earn money for his boy's first communion.

But the protest has international implications too. If the worries about the long-term effects on health of these masts spread to the rest of Ireland, the call for a full investigation would be inescapable; the same studies that are casting doubt over the safety of low-level microwaves also implicate other radio frequencies.

If that happens, how long will it be before British Juliannes are cycling through the darkness to picket lines around British hills?

(Photograph omitted)