Berkshire Hathaway is to buy $US5 billion of stock in the Wall Street bank Goldman Sachs.
In a statement, Goldman Sachs said on Tuesday that Berkshire Hathaway could double its stake within five years.
Under the terms of the agreement, Berkshire Hathaway is buying $US5 billion of perpetual preferred stock and will have the option of buying $US5 billion of common stock "at any time for a five-year term".
Berkshire Hathaway is run by billionaire Warren Buffet.
Shares of Goldman rose $US10.65, or 8.5%, to $%135.70 in after-hours trading following the announcement.
The investment is Mr Buffett's second major purchase in less than a week. On Thursday, his MidAmerican Energy Holdings Co affiliate agreed to buy power supplier Constellation Energy Group Inc for $US4.7 billion.