Does the key to your heart lie in your genes? Yes, says an online matchmaking company that pairs up singles based on differences in their DNA.

According to Eric Holzle, founder of ScientificMatch.com, research shows that people (and animals) are attracted to potential mates who have different immune system genes, which ensures healthier relationships and children.

Scientists have long believed that these genes emit specific odours, which a potential mate would find either terribly sexy or downright smelly.

Holzle first got the idea for his website when he learned of a Swiss study he dubbed "the sweaty t-shirt experiment," which tested for a link between genes, scent and mating preferences.

The researchers asked male subjects to sleep in a T-shirt, which would then carry the wearer's natural body fragrance.

"(The researchers) found that the correlation was if the immune system genes between the T-shirt wearer and the T-shirt sniffer were very similar, then the T-shirt didn't smell very good," Holzle told Canada AM earlier this week.

"And if the immune system genes were very different between the two, then the T-shirt was rated as smelling very attractive. So opposites attract. When I heard about the study I figured it was a great premise on which to base a dating service."

For a fee of US$2,000, which guarantees a lifetime membership to the site, users simply drop a cotton swab they have wiped on the inside of their cheek into the mail. A laboratory analyzes the immune system genes, uploads the information to the site, and the user is then free to browse and contact matches.

The site, which went live in Dec. 2007, does not make public the number of customers who have signed up, nor does it track the amount of couples that have been successfully matched.

But it does cite more than 40 peer-reviewed scientific studies that "substantiate the various benefits that you get from this kind of chemical matching," Holzle said.

The site boasts six benefits of scientific matching:

• A better chance of liking your potential partners' natural body fragrances;
• A more satisfying sex life;
• More orgasms for women during sex;
• A lower infidelity rate;
• Having healthier children with stronger immune systems;
• Higher fertility rates.

"Fertility is an amazing benefit and it affects the couples in two different ways," Holzle said. "Number one, it's easier to get pregnant in the first place, and number two, there's a lower rate of miscarriage once the couple does get pregnant when their immune system genes are matched in this way."

The service will match both heterosexual and same-sex couples, but it does have some restrictions, including the fact that it is only available, for now, in the Boston area.

Women on the pill cannot sign up because oral contraceptives trick a woman into thinking she's pregnant, which causes her to seek out people with similar genes, Holzle said.

People who were not raised by their biological parents very early in life are also exempt from signing up, Holzle said, because research has shown that adoptees often seek out people based on their adoptive parents' immune system genes.