The Purchasing Managers Index prepared by the Institute of Supply Management pegged the overall manufacturing index at 51.5 percent, up from 49.6 percent in August.
The index uses 50 percent as the dividing line between growth and contraction.
In August, both the overall index and the new orders component index were in the red. Both climbed into positive territory in September with new orders rising from 47.1 percent in August to 52.3 percent in September.
The institute's employment index stayed positive with growth accelerating. The employment measure rose from 51.6 percent to 54.7 percent.
International research firm Markit reported similar figures, but came out with a glass-half-empty conclusion.
For Markit, which had the U.S. PMI at 51.5 in August, the September reading of 51.1 was not only disappointing but the lowest level in three years by its monthly calculations.
Markit said the PMI "was consistent with only a modest expansion of the U.S. manufacturing sector."
Markit said new orders rose from 51.9 percent in August to 52.3 percent in September while its jobs index fell from 52.4 percent to 51.9 percent.
The ISM, meanwhile, said 11 of 18 manufacturing sectors were reporting growth, including textile mills, food and beverage industries, printing and related businesses and wood products.