From a woman's point of view, friendship keeps you emotionally healthy. And that's not a subjective opinion. Scientific studies have proven friendship can protect against psychological problems. But friendship can be a problem for men. Many men are so reliant on the women in their lives to provide a social environment for them that they have no other resources on which to fall back if the relationship fails. "If you're in a relationship, your friends are your partner's friends too. When the relationship breaks up, men seem to lose all their friends," says Conor, a separated man in his 30s.

Billy (50), a rigger in RTE, comments: "When you marry, all your old friends are left behind and you go into your wife's circle of friends. Men are also very competitive, so that they are always looking at each other to see who is earning the most and who has the best car so it is impossible to get past that.

"I have male acquaintances that I drink with, sail with and go to matches with, but they are not friends. I have met my brothers for a pint, but that connection has fallen off and there is a distance there. Am I lonely? You could call it that. A real deep-down friendship is hard to find," he says.

What is it about men and friendship? Michael Hardiman, psychologist and author, says: "A lot of men find it difficult to experience the benefits of deep friendship. They may feel great affection and loyalty, but tend not to express it. Men have permission to express their feelings for one another only in situations of great adversity and danger, such as war. All the research into heroism shows that men are protecting each other, rather than fighting for a cause.

"When men are allowed to show fear and vulnerability, then the deepest connections can be expressed. Otherwise, men find it difficult to express friendship directly. Men can build extraordinarily deep bonds, but they don't name them. It's taboo to name your feelings."

But men are changing. Fifteen years ago, TV footage of football matches would show men shaking hands, at most, in the moment of victory. Today men dance around, hug one another and even plant kisses on each other's lips. But such affection is permissable only on the sportsfield - it still doesn't mean that men are sharing their souls with each other.

"In Western culture, physical affection between men is taboo except in extraordinary situations," says Hardiman.

For a woman to spend an evening as men do, in the company of friends gossiping about sports, business, cars and who is earning what - without any reference to their interior lives - would be regarded as rather cold. However, Rob Weatherill, psychologist and author, thinks that women are judging male friendship according to female standards. He doesn't see why men should have to disclose their souls the way women do if that doesn't feel right for them.

"Men have their own ways of being intimate with one another and they shouldn't be judged according to women's perceptions," he argues.

Many men get around the male-to-male barrier by having their deepest friendships with women. "Some of my friends would be female and I learn considerably more from them than I do from my male friends," says John, a single man in his 20s.

So is the psychological safety valve for men friendship with women? Maybe that's unfair, as illustrated by the following anecdote.

Two men, both in their 40s, had experienced similar life-threatening illnesses but had not discussed their experiences, as women would, with friends. Their wives arranged for them to meet and talk. The men talked about football, music, their college days and property prices, but not a mention was made of their shared crises. The wives thought the conversation had been a loss, but a few days later, both men confided that the conversation had made them feel much better.

Perhaps there is an elegant, dignified mystery of male intimacy which women cannot judge by their own standards, in which the most important, intimate exchanges are contained in what is left unsaid.