 Pharmacy benefit managers are kind of the middlemen of the pharmaceutical supply chain, says John DeKenn, a director in the health care team at the U.S. Government Accountability Office, another federal agency that's looked into PBMs. It's really these PBMs that are acting on behalf of the health plans that may be negotiating with the pharmacies in terms of participating in their health plans network, in terms of the prices that the pharmacies are reimbursed, setting rebates with drug manufacturers.