Now that he's taken care of selling ImClone Systems to Eli Lilly (NYSE:LLY), Carl Icahn is off to other biotech adventures

A quick look at Icahn and his fund's SEC filing shows that he's increased his stake in Biogen Idec (NASDAQ:BIIB) and Amylin Pharmaceuticals (NASDAQ:AMLN), perhaps for different reasons.

Icahn has been pretty clear about his intentions to get Biogen sold to the highest bidder -- even though breaking up the company would be very difficult. It's anyone's guess, but I'd imagine that he's more likely stocking up for another proxy fight than just grabbing cheap shares.

Amylin is an entirely different story. As I said when Icahn originally purchased shares in the diabetes specialist, I have a hard time seeing Icahn getting Amylin sold off. The company is partnered with Eli Lilly to sell its main drug Byetta, and I don’t see anyone getting in a bidding war with Lilly. It's more likely that Icahn sees Amylin as a cheap value play, since potential pancreatitis side effects with Byetta have caused the company's stock to crash in the last few months.

Icahn also opened a position in Exelixis (NASDAQ:EXEL), which I'd also put in the cheap-but-unsellable category. Between its partnerships with GlaxoSmithKline (NYSE:GSK), Genentech (NYSE:DNA), and Bristol-Myers Squibb (NYSE:BMY), it would be hard to make Exelixis appealing to any one company.

From Icahn to Buffett, guru investors’ holdings make pretty decent watch lists, but when it comes to an activist investor like Icahn, you also have to try and figure out what his intentions may be. We'll have to wait and see what Icahn does, but my guess is that he keeps badgering Biogen and leaves Amylin and Exelixis alone -- for now.

Eli Lilly and GlaxoSmithKline are Income Investor selections. Exelixis is a Rule Breakers pick, and the Fool owns some shares. Biogen Idec is a Stock Advisor recommendation. Try any of our Foolish newsletters today, free for 30 days.

Fool contributor Brian Orelli, Ph.D., would like to go on an adventure with Bill and Ted. He doesn't own shares of any company mentioned in this article. The Fool's disclosure policy went on an adventure with Tom and David Gardner during the dot-com bubble, but it's not allowed to talk about it.