Their work is usually done in secret, and it is often frowned upon. They may be called in to deal with bizarre paranormal phenomena – holy water boiling up unaccountably, prayer cards suddenly going up in flames and crucifixes flying around living rooms.
Ireland's exorcists tend to shun publicity, but they have been given new recognition and respectability during the papacy of Benedict XVI.
This week, the world's best-known exorcist, Gabriele Amorth, expressed his gratitude to the retiring Pope for his encouragement.
The man, who casts out demons for the Diocese of Rome, recalled how Benedict had welcomed exorcists from all over the world at a special audience.
Ireland currently has at least three practising Catholic exorcists, who are given the task of banishing evil spirits and things that go bump in the night.
Fr Pat Collins, a Vincentian priest based in Dublin, is the most prominent cleric in the field and has been called in to deal with many cases of demonic disturbance around Ireland.
According to church authorities, exorcisms are also carried out by a Jesuit priest based in Galway and a Capuchin friar in Carlow.
Fr Pat Collins declined to talk publicly about his work this week. However, it is believed that he receives regular calls from tormented people, and the number of cases has increased recently.
The priest is often contacted because of unexplained phenomena in homes, such as objects moving about or electrical gadgets turning on and off.
Some householders are so terrified that they flee their homes. Others suspect that someone is possessed.
In one case in Co Derry, Fr Collins and a Church of Ireland exorcist, Canon William Lendrum, were called in to cast out a "malevolent spirit".
A young couple were frightened and moved out of their house after rosary beads and a crucifix were said to have flown around a room.
Holy water was reported to heat to boiling point, and then just as quickly, it froze.
A prayer card to St Michael the Archangel is said to have burst into flames as the man of the house started vomiting.
At the scene, Fr Collins and Canon Lendrum said a cleansing prayer, and this supposedly helped to rid the home of the undesirable spook.
The authors, David Kiely and Christina McKenna, documented 10 cases of Irish exorcism in their book, The Dark Sacrament.
Christina McKenna said she
was encouraged to write the book after her own experience of an exorcism
as a girl in Derry.
"When I was 11 we had a poltergeist in our home.
After my great-aunt died we heard a tapping sound under the bed where
she had been. Priests came and prayed, but they didn't have the power to
stop it. A special exorcist came from England and he performed some magic in the room for a long time and we were free of it."
McKenna said exorcism in Ireland was very different to the image popularised in Hollywood.
"I have never come across a head spinning like in the film The Exorcist," she said. "Usually
the priest would deal with the problem by saying prayers. They would
bless the house, and bless the victim with holy water."
According to Irish experts in the field, cases of "complete possession by the devil" are rare.
In
the vast majority of cases, according to one Dublin priest, only a part
of the personality is subject to demonic influence. A simple exorcism
is all that is required.
In more serious cases of
suspected possession, the case can only be investigated by a trained
exorcist with the permission of a bishop.
A spokesperson
for the Irish Catholic Bishops' Conference said: "The
church recognises exorcism and there is an updated rite that has been
put in place. Courses on exorcism for priests have been run in Rome."
Critics of the practice believe that there is a danger that medical conditions could be treated as demonic possession.
However, church authorities say they are on their guard against this.
One
diocesan church official said: "We don't have a diocesan exorcist, but
we normally refer people to one or two priests with training and
expertise in that area. In most cases it will emerge
after meetings that it may be a medical, psychiatric or psychological
problem and they are referred to medics with expertise in that area."
No
Irish exorcist is as prolific as the Italian Gabriele Amorth, former
president of the International Association of Exorcists. He claims to
have cast out the demons of 70,000 people and has given some vivid
descriptions of the devil and all his works
"I have seen
many strange things," Amorth said of one incident. "The devil told a
woman that he would make her spit out a transistor radio, and lo and
behold she started spitting out bits and pieces of a radio."
Amorth
also caused a stir when he suggested that Pope Benedict had unwittingly
carried out an exorcism on two men at a public event in St Peter's
Square. Their teeth reportedly chattered and they trembled as the Pope
blessed them.
Some of Amorth's claims are treated with
scepticism within the church, and not all priests believe it is
desirable to dwell on casting out demons.
But exorcism has only grown and grown under the current Pope.