A Look Inside the eHarmony Love Lab

Feb. 13, 2008 — -- Monica Breeden says she owes her trip down the aisle to eHarmony.com, which claims to be the most successful online dating site.

EHarmony has about 19 million single members looking for love, and a national Harris poll found eHarmony's site is responsible for about 44,000 weddings a year and more than 100,000 babies born so far from the site's cybermatchmaking.

"Whatever they're doing in the background worked for us," said Breeden, who met her husband, Josh, through eHarmony.

EHarmony CEO Greg Waldorf says the site's success is based on much more than luck. "Behind that site is incredible research, incredible science," Waldorf said.

EHarmony uses a mathematical algorithm that picks partners based on a 258-question personality test that asks things like, "Do you have a messy room?" or "Do you get angry easily?"

The questions come from the company's study of 5,000 married couples. The findings show the more alike you and your partner are, the longer your marriage will last.

"Opposites attract, then they attack," said Galen Buckwalter, the vice president of eHarmony Research and Development. "Over time, if you have differences you're going to constantly have to negotiate them. Those differences start to be not so cute."

For the first time, ABC News cameras were allowed inside eHarmony's secret "love lab" in Pasadena, Calif., where researchers watch their subjects' every move hoping to pinpoint what makes good chemistry.

EHarmony scientist Gian Gonzaga studied the body language of nine strangers — the lab "love rats."

"What we're looking for are cues that are linked to sexual desire, like biting or licking the lips, and other cues linked to love, like gesturing with the hands or nodding," Gonzaga said.

Watching subjects Catherine and John, Gonzaga said that they didn't appear to have much chemistry.

"They're not moving around very much," Gonzaga said. "They are both sitting straight up and away from each other."

On the other hand, Catherine and Lee seemed to have a definite spark. In fact, he gave her a kiss on the cheek after their meeting.

"She flipped her hair back right at that moment, and you see how they're moving in unison. As she's moving forward, he's moving forward. That's the kind of mirroring and posturing we see with couples who are getting along very well," Gonzaga said.