The largest-ever European biotech IPO - by Circassia Pharmaceuticals plc - plus three new filings have buysiders thinking the crack in a European IPO window could be widening. But if Circassia doesn't perform, it could once again put public investors off U.K. biotech for years to come.

On March 13, Circassia raised £200 million ($334.2 million) through the sale of 64.5 million shares at 310p in an IPO on the London Stock Exchange. The price valued Circassia at £581 million ($970.8 million). Underwriters are JPMorgan; Peel Hunt; Canaccord; and Shore Capital Stockbrokers.