NEW YORK (CNN/Money) - A measure of U.S. service-sector activity stayed high in August, the nation's purchasing managers said Thursday, beating analysts' expectations and matching July's record level.

The Institute for Supply Management said its index of non-manufacturing business activity in August matched July's unrevised 65.1 reading. Economists, on average, expected a reading of 63, according to a Reuters poll.

July's index had been the highest since the group's survey began in July 1997.

U.S. stock prices turned higher after the report, while Treasury bond prices gave up some earlier gains.

In part because it's only six years old, the non-manufacturing ISM index doesn't get as much attention or credit as the manufacturing ISM, which posted a strong gain in August.

Still, the service sector is critical to the economy, making up more than 85 percent of gross domestic product (GDP) and employing more than 85 percent of all U.S. workers.

The ISM's "new orders" index rose to 67.1 from July's 66.9, indicating the pace of new orders increased in August.

Its employment index rose to 51 from July's 50.7, indicating the pace of hiring was picking up, and its price index soared to 55.7 from 50.6.