A large acquisition and the start of the new Medicare Part D prescription drug program boosted profits at a managed care giant during the second quarter.

UnitedHealth Group Inc., Minnetonka, Minn., is reporting $974 million in net income for the latest quarter on $18 billion in revenue, up from $770 million in net income on $11 billion in revenue for the second quarter of 2005.

The recently completed acquisition of PacifiCare Health Care Systems Inc., Cypress, Calif., contributed to a gain in enrollment as well as in revenue.

The company ended the quarter providing or administering health coverage for 17 million U.S. residents, up from 13 million a year earlier.

The number of participants in UnitedHealth’s 6-month-old Medicare drug program increased to 5.7 million at the end of the second quarter, from 4.5 million at the end of the first quarter.