More than 550 health professionals and organizations have signed a letter to McDonald's Corp. asking the maker of Happy Meals to stop marketing junk food to kids and retire Ronald McDonald. The letter, slated to run in the form of full-page ads in six metropolitan newspapers around the country on Wednesday, acknowledges that "the contributors to today's (health) epidemic are manifold and a broad societal response is required. But marketing can no longer be ignored as a significant part of this massive problem. We are committed to responsible advertising and take our communications to children very seriously," McDonald's said in a statement. "We understand the importance of children's health and nutrition, and are committed to being part of the dialogue and solution..." The campaign is organized by the nonprofit watchdog group Corporate Accountability International...The McDonald's letter...has been signed by such groups as the American Academy of Child and Adolescent Psychiatry and the Chicago Hispanic Health Coalition, as well as by well-known nutritionists and doctors...The campaign also includes...[a] shareholder's resolution...[calling] on McDonald's to tally the financial impact of fighting various measures like the San Francisco ordinance passed last year that established nutritional standards for kids' meals that come with toys.