Trying to accurately value a biotech stock isn't just difficult -- sometimes it seems downright worthless. After all, how can investors even try to value a company that hasn't booked a dollar in revenue?

In the following video, Brenton Flynn walks through a commonly used method for valuing biotech stocks and offers a word of caution for investors in companies like Arena Pharmaceuticals (NASDAQ:ARNA), Threshold Pharmaceuticals (NASDAQ:THLD), and Pharmacyclics (UNKNOWN:PCYC.DL), which are waiting on lucrative milestone payments.