Manufacturing added 10,000 jobs in the month, finance another 7,000. The construction sector added 15,000 new jobs, the firm said.
Firms with under 50 employees gained the most jobs in the month -- 50,000. Medium-sized firms with 50 to 499 workers added 26,000 jobs. Firms with more than 500 workers added 43,000 positions, ADP said.
The trend since December has been a a disappointment, however. In the final month of 2012, using ADP figures, private sector employers added 215,000 jobs. In January, they added 192,000. In February, 198,000 jobs were created. In March, that had dropped to 158,000.
Economists had predicted for April that ADP would announce a gain of 150,000 jobs.
"During the month of April 2013, U.S. private sector employment increased by 119,000 jobs, representing the slowest pace of expansion since September 2012," Carlos Rodriguez, president and chief executive officer of ADP, said in a statement.