The number two and three US health website networks are to merge to take on the might of market leader WebMD.

Waterfront Media, number two, will merge with Revolution Health Network, number three in the market, to create a network of 24 health web sites. Terms of the agreement were not disclosed.

Waterfront Media operates the Everyday Health Network, a collection of health Web sites that reported 14m unique visitors in July 2008, making it the second most popular US health information destination. Revolution Health sites collected 11m million unique visitors, the third-highest total online.

By comparison, market leader WebMD had 23m unique visitors during that same period.

Waterfront Media co-founder Benjamin Wolin will be chief executive of the new company while Revolution Health founder and ex-AOL boss Steve Case, will join the board of the new firm.

The new company will operate as Waterfront Media and will integrate the Revolution Health sites into the Everyday Health Network.

According to Benjamin Wolin, co-founder and CEO of Waterfront, the combined company will have a more than €73m $100m revenue in 2009.

Case, a co-founder of America Online, told the Wall Street Journal "the merger of Waterfront Media and Revolution Health Network builds on each company’s complementary strengths to create a new industry powerhouse."