A regulatory filing yesterday showed Berkshire, which is owned by billionaire investor Warren Buffett, now holds 4.5 million shares-still less than 1 percent of the health insurer.
Buffett has been accumulating the stock for months. In the second quarter, he quadrupled his WellPoint holdings.
Investors have speculated that Berkshire might want to acquire WellPoint outright. The Indianapolis company has a stock market value of $46.6 billion.
Berkshire said in last year's annual report that it needs to make big acquisitions to generate "truly satisfactory" earnings growth, and Buffett in May said that he is looking to spend $40 billion to $60 billion.
Buffett also has said that Berkshire is looking for companies with consistent earnings, simple business plans, good return on equity and minimal debt.