The greatest danger to public health might be "checkbook science": research intended not to expand knowledge or to benefit humanity but to sell products. Much of the media coverage of health news stories is based on public relations efforts on behalf of the companies that sell the products, including pharmaceutical companies, diet clinics, or doctors selling new techniques. The author presents three case studies of how companies selling medical products effectively but invisibly shaped recent news coverage of medical products: fen-phen diet pills, breast implants, and hormone replacement therapy. All involve subtle strategies whereby physicians and other experts paid by corporate interests are influential because they are perceived to be objective medical experts. Articles in prestigious medical journals are sometimes ghostwritten by individuals paid by companies or are based on biased analyses or interpretations shaped by corporate interests. Nonprofit organizations that tout the benefits of specific medical products also may be part of the public relations efforts of the companies making the product. Meanwhile, important newsworthy studies are ignored by the mass media when corporate interests do not publicize or pitch the results to influential reporters and producers.