In hot equity markets, U.S. companies traditionally have not been bashful about floating an IPO and then returning in short order with a follow-on. But European biotech companies still face the challenge of convincing investors that it's important to seize the moment when money is available. The current follow-on situation in Europe looks tight, and it is near on impossible to return to market within U.S. time scales given hurdles posed by regulators, investor attitudes, liquidity and a basic demand for new public companies.

The current financing window has not been particularly accommodating to follow-on deals in the U.S. either. But the list includes three U.S. companies that raised successful follow-on financings within six months of their IPOs, all in March. In Europe, two IPO companies waited nearly a year before going back to market (see "Double Dipping").