Warren Buffett's Berkshire Hathaway purchased 1.13 million more shares of DaVita HealthCare Partners this week, raising its stake in the kidney dialysis company to 17.7 percent.
The purchases bring Berkshire's total stake in the company to 37.62 million shares. At Wednesday's close of $67.50, the stock had a market value of $2.54 billion.
An SEC filing said the purchases were made from Monday through Wednesday at prices between $66.12 and $68.
Berkshire has been buying DaVita shares since the fall of 2011. Last May, it agreed not to increase its stake above 25 percent. It also promised it would not push for board seats or launch a proxy fight.
This is not a Warren Buffett investment. Portfolio manager Berkshire's Ted Weschler has been buying the shares and signed the agreement with DaVita.
(Read more: Berkshire Hathaway's 15 biggest stock holdings)
In a separate filing, Buffett's business partner Charlie Munger said he has given 100 shares of Berkshire Class A to Harvard-Westlake School, an independent co-ed prep school in Los Angeles with about 1,600 students enrolled in grades 7 through 12.
Munger is a longtime benefactor of the school, which is home to the Munger Science Center.
In an interview with the Berkshire-owned Omaha World-Herald last June, the 90-year-old Munger said he was "deliberately taking my net worth down" by making donations to various schools because "I won't need it where I'm going."
His largest gift to date is the $110 million worth of Berkshire stock he gave to the University of Michigan last April.
—By CNBC's Alex Crippen. Follow him on Twitter