The acquired firm, Pharmaceutical Resource Corporation, specialises in Phase III-B and IV trials, as well as pharmacovigilance and drug safety - areas where INC had been looking to gain new expertise.
"With the addition of PRC, we are able to offer our customers a greater depth of late-phase clinical trial experience," said James Ogle, INC's chief executive officer.
Pharmaceutical companies are often required to carry out late phase studies by the Food and Drug Administration (FDA) after a drug has received approval in order to gather more clinical information.
With several recent high profile concerns over drug safety, such as in the case of Vioxx, these studies are being requested by the FDA more and more often and the late phase CRO business is booming.
The new company was bought for an undisclosed sum and brings INC's sites in the US to a total of five.
INC has been going through a period of expansion of late, moving into new US headquarters in Raleigh where it is currently in the process of adding 100 new workers to the site.
The company also opened new offices in France, Russia and the Ukraine earlier this year, as well as acquiring an oncology firm last December.