Stocks are mixed at the opening of trading after commodity prices rose, along with worries about Greece's debt problems.
Crude oil is up 2.6 percent, copper is up 1.5 percent, and silver is up 5.7 percent. The partial recovery from last week's sell-off in commodities is lifting stocks of energy companies and metal miners.
But Standard & Poor's also cut Greece's debt rating further into junk status, raising fears about the value of Greek bonds.
The Dow Jones industrial average is up 6 points to 12,645. The S&P 500 is up less than 1 ponit to 1341. The Nasdaq composite index is down 3 points to 2,824.
European markets are falling. France's CAC 40 index is down 1.1 percent, and Germany's DAX is down 1 percent.