Take note, providers served by Palmetto GBA: the HHH Medicare Administrative Contrac-tor has changed how it mails additional development requests (ADRs). Now you should be looking for a white envelope in the mail rather than a yellow one, Palmetto explains on its website. Plus: "It is possible that a provider may receive an ADR request prior to receiving their probe notification letter," Palmetto adds. Remember: "If you receive an ADR, it is important that you respond promptly," the MAC stresses. Non-response to ADRs is repeatedly one of the top denial reasons for claims.