That brought UBS’s total write-downs to nearly $40 billion  more than any other bank’s  and UBS expects to post a first-quarter loss of $12 billion. But its plan to raise new capital quashed fears that the bank, based in Zurich, was facing deeper threats because of the subprime woes.

UBS’s financial woes caused another casualty, however, in its executive suite. UBS’s longtime chairman, Marcel Ospel, abruptly resigned Tuesday after months of criticism from shareholders.

Last summer, Peter Wuffli, the bank’s chief executive, was among the first of a series of high-profile financiers to be forced out by subprime losses. Now, with Mr. Ospel’s departure, UBS has joined American giants like Merrill Lynch and Citigroup in cleaning house at the top. UBS said its general counsel, Peter Kurer, would succeed Mr. Ospel.

Lehman Brothers, the investment firm hit by worries about its ability to weather the downturn, is already close to raising $4 billion in fresh funds from investors. That is far more than the $3 billion it said it would seek, which analysts read as evidence of confidence in its future.

Financial stocks in Europe, including those of UBS, Deutsche Bank and Société Générale, as well as those of their American counterparts  including Lehman, Citigroup, JPMorgan Chase, Merrill Lynch, Bank of America and Goldman Sachs  surged Tuesday.

While the willingness of investors to put up fresh cash for Lehman and UBS underscores that they are in a stronger position than Bear Stearns, which was forced to sell itself to JPMorgan last month, the mortgage mess remains a threat.

Not only are tens of billions in troubled home loans that remain on the books of banks hard to value, but potential buyers for these assets have evaporated in recent months amid fears that a recession in the United States might threaten swaths of the credit market that were previously thought to be safe.