Exchange-traded funds tracking homebuilders and REITs were all falling hard for a second straight session Monday, as investors continued to fret about the health of credit markets.

Shares of American Home Mortgage ( AHM) slid 36% before the stock was halted following word the company has filed for bankruptcy protection. On Friday, American Home Mortgage said it would slash roughly 90% of its work force.

Among REIT-related ETFs, the iShares FTSE NAREIT Mortgage REITs ( REM) was dropping $2.04, or 6.4%, to $30.07. The Ultra Real Estate ProShares ( URE) gave back $1.53, or 3.8%, to $38.88. The SPDR Dow Jones Wilshire International Real Estate ( RWX) ETF was tumbling 84 cents, or 1.4%, to $59.05.

Homebuilders were feeling the crunch as well. Standard Pacific ( SPF) was diving by 19%, while Beazer Homes ( BZH), Centex ( CTX), Hovnanian ( HOV) and Meritage Homes ( MTH) were losing 3.5% or more.

The iShares Dow Jones U.S. Home Construction ( ITB) was shedding 85 cents, or 3.4%, to $24.30. The SPDR S&P Homebuilders ( XHB) was lower by 77 cents, or 3%, to $24.73.

Energy-related ETFs were also getting crushed as the September front-month crude contract slid $2.18 to $73.30 a barrel. The Ultra Oil & Gas ProShares ( DIG) was giving back $2.56, or 2.9%, to $85.76. The SPDR S&P Oil & Gas Equipment & Services ( XES) slid $1.19, or 3.4%, to $34.20. The PowerShares Dynamic Energy ( PXI) was lower by $1.09, or 3.4%, to $30.69.

On the flip side, bundled securities tracking the health care sector were among few winners to start the week. Before the opening bell, UnitedHealth ( UNH) raised its guidance for 2007 following a favorable Medicare adjustment. The stock was recently up 2%.

The Ultra Health Care ProShares ( RXL) was higher by $1.06, or 1.6%, to $67.18. The iShares Dow Jones U.S. Healthcare Provider ( IHF) was up 81 cents, or 1.5%, to $56.56. The Health Care Select Sector SPDR ( XLV) tacked on 46 cents, or 1.4%, to $34.14.

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