Wall Street watchers have been saying for months that the biotech IPO window won't close in the U.S. until investors stop making money in the aftermarket. With the double-whammy of global events and profit-taking, this notion is now being put to the test.

The U.S. IPO group - which consists of 55 deals that jumped through the IPO window since Oct. 1, 1999 - had traded up 89 percent through the end of the third quarter. But it's taken only two weeks to cut that number in half, with the gain now down to 43 percent. In the first two weeks of the quarter, all but one - Tanox Inc. (TNOX, Houston, Texas) - have traded down.