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UnitedHealth Group shares have soared almost 30% since Berkshire Hathaway's disclosure in mid-August that it had purchased a bit more than 5 million shares between April 1 and June 30.

Minutes before that SEC filing , UNH closed at $271.49. On Friday, it ended trading at $352.51.

Although UNH had already started to bounce from its lowest close of the year of $237.77 on Aug. 1, Berkshire's endorsement of the troubled stock is responsible for at least a sizable chunk of its recent gains. Zoom In Icon Arrows pointing outwards

It is not clear, however, whether Berkshire's investment is profitable (on paper) at

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