The Standard & Poor's 500 index held on to a record level, but the Dow Jones industrial average edged lower.
Merck fell after the drugmaker sharply lowered its profit forecast and reported a plunge in third-quarter earnings.
The S&P 500 was up half a point at 1,760 in midday trading Monday. The Dow fell 15 points to 15,555. The Nasdaq composite was down 10 points to 3,933.
Homebuilders fell after the number of Americans who signed contracts to buy previously occupied homes fell in September to the lowest level in nine months, reflecting higher mortgage rates and home prices.
The yield on the 10-year Treasury note was unchanged at 2.51 per cent.