What are the 10 biggest companies in the United States? Put that question to a group of younger people, and they’re likely to rattle off tech giants such as Google, Amazon, and Facebook. Older people might mistakenly believe that manufacturing still leads the pack with postwar Goliaths such as Ford or General Electric. Oil companies (ExxonMobil, BP) and megabanks (Citi, Wells Fargo) seem obvious contenders.

Yet regardless of who’s doing the guessing, I suspect it would take a very long time before anyone mentioned UnitedHealth, McKesson, and AmerisourceBergen. Who, beyond each firm’s array of boardrooms and back offices, has even heard of them? Nevertheless, they are ranked as 6, 7, and 10, respectively, on this year’s Fortune 500 ranking of the biggest companies by total revenues. If you add CVS-Caremark (#8), four of the 10 largest actors in the economy are distinctly low-profile middlemen in the rapacious and wholly inadequate profit-driven system of health care in the U.S., which constitutes an astounding 18 percent of our gross domestic product.

It doesn’t take much digging to figure out where all that money is going. The top 25 entries in the Fortune list also include Walgreens and Cardinal Health. Mail-order pharmacy service Express Scripts also cracked the top 25 in 2018 but was purchased by Cigna and disappeared in this year’s rankings. That puts effectively seven of the top 25 companies in the nation’s economy in the health care industry—with the vast majority of their revenue derived from administrative activities rather than productive ones, such as manufacturing pharmaceuticals, supplying insurance, or directly providing service to patients. They represent a fast-burgeoning rentier segment of our health care bureaucracy that operates behind the scenes to increase profits, reduce company costs, and generally ensure the toxic combination of expensive and poor service that American health care consumers experience.

UnitedHealth is the only insurer among these companies, and it’s presently under investigation in several states for its refusal to pay out on substance abuse and mental health claims. Walgreens and CVS are widely recognized dispensers of retail pharmaceuticals. But then there’s … well, what exactly does AmerisourceBergen do? That company is among the leading firms now raking in enormous profits by processing paperwork and moving prescription drugs between manufacturers and user-end pharmacies. Most Americans have never even heard of these corporations and have no idea that they are bigger than such familiar Wall Street names as JP Morgan Chase, General Electric, and Verizon. They like that anonymity.

AmerisourceBergen bills itself as a “healthcare solutions company.” McKesson is more honest, using the telling terms “wholesale” and “pharmaceutical distribution” in its boilerplate prospectus materials. Express Scripts and Caremark (now part of CVS) are “prescription benefit management” specialists—that is, they have burrowed into a layer of bureaucracy and profit-skimming that unfolds between the moment your doctor hands you a prescription and the point when your pharmacist dispenses it. Cardinal Health is a wholesaler, a distributor of pharmaceuticals and medical products—although, unlike most of these middleman operations, it does manufacture some medical devices in-house.