Acevedo said it was impossible to extrapolate from their study what percentage of long-lasting couples might register the same intensity of emotion as her 17 subjects. But she said a previous phone survey of several hundred people in long-term relationships she and Aron conducted found about 35 percent rated their feeling for their partners as very intense. "We were shocked," she said. "We hadn't predicted it would be that high."

Keith Davis, professor emeritus of psychology at University of South Carolina, said other studies support Acevedo and Aron's research. "I think popular literature underestimates how many retain a high level of intense emotional investment with their partners."

TOGETHER, FOREVER

—Barbara Jean and Eugene Williams of Roosevelt, N.Y., have been married 51 years. They have five children and 12 grandchildren.

Eugene Williams, 72: "The love hasn't changed. What has, if anything, has changed, it's the relationship, in terms of how I understand (his wife). It's just gotten better. ... Of course, the reason is we have always trusted each other's feelings. "

Barbara Jean Williams, 71: "Today, he is the same and he makes me feel that I am one of the most special persons that he's ever encountered. I love him for that. "

—Carole and Walter Wozniak of Seaford, Fla., have been married 50 years. They have two daughters and two grandsons.

Carole Wozniak, 71: "You're with somebody for 50 years, you share the same things, you enjoy the same things. That, of course, makes the passion. It changes a little, but I feel the same. When I saw my husband 52 years ago, it was a chemical reaction. ... I still feel that way today."

Walter Wozniak, 80: "I met her at a dance at the Valley Stream Park Inn. ... I still love her like I did when we were first courting, I would say. The thing is that before you love somebody, you've got to like the person. You've got to have respect for them, and they have respect for you."

—Marilyn and Bob Mangan of Massapequa Park, N.Y., have been married 35 years. They have three children and one grandchild.

Marilyn Mangan, 61: "It's different. I don't think it's the same kind of passion. It's not as constant. It's more you learn to appreciate each other more. ... There are times when it's just so wonderful you know why you have been there that long."

Research has found that passionate, long-lasting relationships generally have several things in common, said Arthur Aron, social psychologist at Stony Brook University:

The couple is not facing terrible "external stressors," such as war or the loss of a child.

One partner is not highly depressed or anxious.

Both know how to communicate with each other.

The couple does new, challenging things together.

When one partner is successful, the other celebrates the success.