Walmart is in talks to expand its already large pharmacy business with the acquisition of insurer Humana Inc. — valued at around $37B.

While the talks between Walmart and Humana are still preliminary, the deal could potentially make Walmart the largest health insurer in the U.S. The two companies also have a pre-existing relationship from partnering on Medicare drug plans, of which Humana is a major provider.

Though Walmart already has pharmacies in 4,700 stores across the U.S. as well as within its Sam’s Club locations, the acquisition could give the retail giant greater access to Humana’s strong base of senior consumers, as well as its data, both of which could help Walmart defend itself against the Amazon onslaught, according to the Wall Street Journal.

Walmart and Humana are not the only ones to consider mergers and acquisitions to compete in the industry. CVS Health and Aetna have also been in discussions for months regarding a $69B merger that has yet to be finalized but is already approved by shareholders.

The moves are in part an effort to strengthen the brands as Amazon continues to seep into the industry. The e-commerce giant recently announced a partnership with Berkshire Hathaway Inc. and JPMorgan Chase to offer more affordable healthcare to employees and expanded a program to provide Amazon Prime to Medicaid beneficiaries at a discounted rate, the WSJ reports.

Humana shares rose 10% to $297 a share after the news broke, while Walmart shares dipped 1% to $88.10, the WSJ reports.