The Institute of Supply Management said its nonmanufacturing index rose to 50.9% in September from 48.4% in August. Any number above 50% indicates growth.
The ISM index had declined for 11 consecutive months.
The ISM said the overall economic outlook remains clouded: "Even with the overall month-over-month growth reflected in the report this month, respondents' comments vary by industry and remain mixed about business conditions and the overall economy."
Among the sub-indexes, the business activity index increased 3.8 percentage points to 55.1% and the new orders index rose 4.3 points to 54.2%.
The employment index indicated ongoing cuts but not as heavy as in prior months, rising 0.8 percentage point to 44.3%.
Services makes up the lion's share of economic activity and employment, and is therefore critical to recovery from the long recession.
Copyright Agence France-Presse, 2009