The Dow Jones industrial average dropped 34.29 to 5,972.73, falling back below the 6,000 mark again after shedding an early 36-point advance. On Friday, the blue-chip barometer halted a four-day losing streak to move back above 6,000.
Decliners outnumbered advancers by nearly a 7 to 4 margin on the New York Stock Exchange, with 893 up, 1,540 down and 824 unchanged. NYSE volume totaled 383.63 million shares, vs. 364.89 million in the previous session.
The Standard & Poor's 500-stock index fell 3.67 to 697.25, and the NYSE's composite index fell 2.28 to 370.98. The Nasdaq composite index fell 6.70 to 1,215.90, and the American Stock Exchange index fell 3.24 to 566.55.
Broad-market measures had surrendered early gains as bond prices slipped, sending interest rates higher. The yield on the 30-year Treasury bond rose to nearly 6.83 percent from late Friday's 6.81 percent.
With the flow of major earnings reports slowing to a trickle, the market spotlight shifted to this week's economic reports, which include key readings on employment costs, the manufacturing sector, and the nation's overall third-quarter growth. The data could provide important clues on whether various inflationary pressures have remained tame enough to avoid an interest rate hike by the Federal Reserve.