American Home Mortgage Investment, once the 10th largest home lender in the United States, filed for bankruptcy protection on Monday.
Last week, Countrywide posted a 33 percent decline in quarterly profit and slashed its 2007 forecast as more homeowners fell behind on payments.
Credit default swaps on mortgage insurer Radian Group also leaped 100 basis points on Monday, to around 500 basis points.
Radian's credit default swap spreads have more than doubled from around 182 basis points last Monday, as concerns about home loans grew, and on increasing speculation that Radian's planned merger with MGIC Investment may fall through.
Bear Stearns' credit default swap spreads also widened around 40 basis points to 200 basis points.
Warren Spector, Bear Stearns' co-president and co-chief operating officer, resigned on Sunday, two days after the bank said in a conference call that it was weathering the worst storm in the financial markets in more than 20 years.