Certain MetroCards now feature ads for Mount Sinai and NYU Langone Medical Center, the first hospitals to buy space on the tiny fare card.
Mount Sinai purchased 50,000 cards, advertising its urgent care site on the card's back.
The cards hit two Upper Manhattan subway stops last week.
NYU Langone Medical Center purchased 1 million MetroCards, with its ad covering both the front and back.
Those cards became available this week at MetroCard vending machines and several stations in Manhattan.
The MTA began selling ad space on MetroCards in 1995.
The agency started selling space on front of the cards two years ago.
An immigration law firm's ad earlier this year became the first Spanish-language MetroCard ad campaign.
The MTA produces 4 million to 5 million MetroCards every month.