New York (CNN Business) Warren Buffett is making an even bigger move into banks.

Last quarter, Berkshire Hathaway ( BRKA ) took a $4 billion stake in JPMorgan Chase ( JPM ), according to regulatory filings posted Wednesday.

Berkshire also grew its investment in Bank of America ( BAC ), Goldman Sachs ( GS ), BNY Mellon ( BK ) and US Bancorp ( USB ) though the company slightly lowered its stake in Wells Fargo ( WFC ).

Buffett has long had a good relationship with JPMorgan Chase CEO Jamie Dimon. He's partnered with the chief executive, as well as Amazon CEO Jeff Bezos, on a new health care venture for employees, and has recommended Dimon's annual investor letter as a must-read.

He said in an interview with Yahoo Finance earlier this year that he regretted not investing in JPMorgan Chase sooner.

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