The proverbial biotech IPO window has been open for some time now, but it appears to have grown to the size of an airplane hangar door, allowing almost any biotech to go public at astonishingly high valuations.

Ultragenyx Pharmaceutical (NASDAQ:RARE) doubled on the day of its IPO and has continued to rise since. As you can probably guess from the ticker, Ultragenyx is developing drugs for orphan indications.

Dicerna Pharmaceuticals (NASDAQ:DRNA) tripled after its IPO. The biotech, which is also focused on rare diseases, pulled back a little since its first day of trading, but Dicerna still trades well above where it priced its IPO.

In the video below, Fool contributor Brian Orelli and health-care bureau chief Max Macaluso discuss the progression of biotech investors from large-cap biotechs to small-cap biotechs and, eventually, as they seek more risk, to companies that have just gone public.