Bear Stearns may have been ultimately taken down by the collapse in the subprime market, but UBS is taking the biggest hit.

The Swiss bank giant announced what a Merrill Lynch analyst called "the big kahuna of legacy write-downs": $19 billion on U.S. real estate and "related structured credit positions." Since October, UBS has written down nearly $37 billion worth of assets.

Because of the latest write-down, the bank expects to report a loss of $12.1 billion for the first quarter. UBS is also seeking $15.1 billion of new capital from shareholders.

Yves Smith on the Naked Capitalism blog points out that UBS lost a third of its equity in a single quarter. "No wonder my trader buddies put UBS high on the list of firms at risk of serious trouble," Smith says.

With those staggering first-quarter numbers, another executive is falling on his sword. Marcel Ospel, the architect of the 1998 merger between Swiss Bank and the Union Bank of Switzerland that created UBS, will leave as chairman. Last summer, UBS began the wave of executive ousters, forcing out its C.E.O., Peter Wuffli. Stan O'Neal of Merrill Lynch, Charles Prince of Citigroup, and James Cayne of Bear Stearns followed in the months to come.

"I have always stated that I ultimately take responsibility for the bank's situation," Ospel said in a statement.

Peter Kurer, who joined UBS in 2001 as general counsel, will succeed Ospel. Haig Simonian of the Financial Times says that the choice of Kurer "indicates a failure to find a more suitable replacement, in spite of intensive contacts with top bankers around the world."

Shares of UBS rose in trading in Switzerland on hope for change with the departure of Ospel and the pursuit of new capital. But Standard & Poor's lowered its rating on the bank to AA- from AA.

"The one saving grace in this is that banks are acting quickly to highlight their exposure," Peter Dixon, economist at Commerzbank, told Reuters. "The quicker the bad news is out in the open, the quicker we can start to repair the problems."

But do UBS shareholders trust that the bank has put the worst behind to stump up another big investment? The bank has already done the sovereign wealth fund well, reaching a deal late last year with the Government of Singapore Investment Corporation and a still-unidentified investor in the Middle East. Its options are running out.