So much of our attitude about life and our capacity to meet life's challenges depends on the quality of the relationships we have, especially our most intimate relationships that when they go sour, life tends to feel bleak. Because the quality of our relationships has a powerful effect on physical and mental balance, as well as our sense of satisfaction in life, it's important that we keep our relationships rewarding and fresh.

The data on divorce provide compelling evidence that we are not succeeding at all. Nearly half of all marriages end in divorce--cohabitation couplings are far likelier to end badly--and of marriages that endure, many are less than happy.

Most people know the value of a good relationship and, no matter how often they have lost at love, keep on hoping. As a result, advice on how to make relationships work fills shelves and shelves of bookstores and hours of talk-show time. Some of it is even good, the product of careful research on happy and unhappy couples.

But of all the elements that contribute to the warm atmosphere of a good relationship, there is one that seldom gets translated into advice or even therapy, yet is something that everyone desires and most people would like more of: Laughter.

It's a safe bet that most of the laughs married couples get come from TV laugh tracks, not from each other. They don't emanate from the relationship. More important, they don't feed it. And if the jokes that make the rounds by email are any gauge, often they are at the expense of it.

But homegrown laughter may be what ailing couples need most. Uniquely human, laughter is, first and foremost, a social signal--it disappears when there is no audience, which may be as small as one other person--and it binds people together. It synchronizes the brains of speaker and listener so that they are emotionally attuned.

These are the conclusions of Robert Provine, Ph.D., a neuroscientist who found that laughter is far too fragile to dissect in the laboratory. Instead, he observed thousands of incidents of laughter spontaneously occurring in everyday life, and wittily reports the results in Laughter: A Scientific Investigation (Penguin Books, 2001).

Laughter establishes--or restores--a positive emotional climate and a sense of connection between two people, who literally take pleasure in the company of each other. For if there's one thing Dr. Provine found it's that speakers laugh even more than their listeners. Of course levity can defuse anger and anxiety, and in so doing it can pave the path to intimacy.

Most of what makes people laugh is not thigh-slapper stuff but conversational comments. "Laughter is not primarily about humor," says Dr. Provine, "but about social relationships."

Among some of his surprising findings:

- The much vaunted health benefits of laughter are probably coincidental, a consequence of it's much more important primary goal: bringing people together. In fact, the health benefits of laughter may result from the social support it stimulates.

- Laughter plays a big role in mating. Men like women who laugh heartily in their presence.

- Both sexes laugh a lot, but females laugh more--126 percent more than their male counterparts. Men are more laugh-getters.

- The laughter of the female is the critical index of a healthy relationship

- Laughter in relationships declines dramatically as people age.

- Like yawning, laughter is contagious; the laugher of others is irresistible.

One of the best ways to stimulate laughter--and it's probably the most ancient way--is by tickling. Tickling is inherently social; we can't tickle ourselves. We tickle to get a response. Or to entice ticklee to turn around and become tickler.

Not only do most people like tickling--ticklers as well as ticklees--most recognize it is a way to show affection. What's more, adolescents and adults prefer to be tickled by someone of the opposite sex.

Tickling is probably at the root of all play and it is inherently reciprocal, a give-and-take proposition. In other words, it exactly represents the basic rhythm of all healthy relationships. Not to mention is triggers sexual excitation in adults.

But tickling declines dramatically in middle age. People begin a gradual "tactile disengagement," reports Dr. Provine. Tickle, touch, and play, so critically intertwined, all go into retreat, although these behaviors are at the root of our emotional being.

So the next time you have an argument with your mate, don't walk out of the room and slam the door. Try tickling your partner instead. (Most ticklish areas, in descending order: underarms, waist, ribs, feet, knees, throat, neck, palms.)

It won't make problems go away. But it can set the stage for tackling them together.