Exchange-traded funds tracking homebuilders and REITs were falling hard Tuesday, as traders continued to fret about the health of credit markets.

Among REIT-related ETFs, the iShares FTSE NAREIT Mortgage REITs ( REM) was dropping $2.13, or 7.1%, to $27.73. The Ultra Real Estate ProShares ( URE) gave back $2.38, or 5.6%, to $39.97. The iShares FTSE NAREIT Residential ( REZ) was tumbling $1.31, or 2.9%, to $44.24.

Homebuilders were feeling the crunch as well. Beazer Homes ( BZH) gave back 9% after Fitch Ratings downgraded its debt again. Meanwhile, Centex ( CTX), Hovnanian ( HOV) and Meritage Homes ( MTH) were losing 3% or more.

The iShares Dow Jones U.S. Home Construction ( ITB) was shedding 76 cents, or 3%, to $25.01. The SPDR S&P Homebuilders ( XHB) was lower by 63 cents, or 2.4%, to $25.27.

Retail-related ETFs were also suffering following disappointing news out of the world's largest retailer, Wal-Mart ( WMT), and Home Depot ( HD).

Excluding items, Wal-Mart said it had earnings of 76 cents a share, matching the Thomson Financial estimate, but the company guided lower for the third quarter and full year. Meanwhile, Home Depot beat estimates by a nickel, but the home improvement retailer said that housing markets should remain soft into 2008.

The Retail HOLDRs ( RTH) was shedding $2.60, or 2.6%, to $97.15. The SPDR S&P Retail ( XRT) was down 94 cents, or 2.4%, to $38.10. The PowerShares FTSE RAFI Consumer Services ( PRFS) was losing $1.15, or 2.2%, to $51.90.

There were few winners during Tuesday's session outside of the biotechnology arena. Earlier, Biogen Idec ( BIIB) said it had positive phase II clinical trial data for its congestive heart failure treatment drug, Adentri.

The First Trust Amex Biotechnology Index ( FBT) ETF was adding 24 cents, or 1%, to $23.95. The Biotech HOLDRs ( BBH) was higher by $1.55, or 1%, to $163.75.