American manufacturing rebounded in September, expanding for the first time in four months despite uncertainty at home and slumping economies around the globe.

The Institute for Supply Management on Monday said its index of factory activity, based on a survey of purchasing managers across the U.S., rose to 51.5 in September from 49.6 in August. It was the first time since May that the index crossed the 50-point threshold that indicates expansion. Gauges of new orders and employment also inched up, boosting hopes that production and hiring will improve in coming months.

The report underscored the relative strength of the U.S. economy compared with Europe, which is mired in recession, and the developing world, where growth has slowed in recent months. The report indicated a pickup in demand for items such as cars and home furnishings, echoing other recent data that suggest the U.S. recovery has regained its footing somewhat after seeming to falter in the spring. Consumer confidence has improved, household spending has grown slowly and the long-depressed housing sector is showing signs of life.

Investors cheered the report, sending the Dow Jones Industrial Average up 77.98 points, to close at 13515.11.

Still, nothing in Monday's report suggests robust growth. The 51.5 reading was barely in positive territory and well below levels earlier in the recovery, when manufacturing was an engine of growth. Exports are falling as demand for U.S.-made goods declines in weakening foreign economies. Actual production—as opposed to orders for future production—fell slightly in September. Overall, the report continued the recent pattern of slow, unsteady growth, with the economy not attaining self-sustaining momentum but not completely stalling out, either.