Research giant GfK said it is acquiring Knowledge Networks, a provider of digital research in the US. The acquisition, terms of which were not disclosed, extends over multiple business units, including healthcare.

The company plans to combine Knowledge Networks’ physicians’ consulting network panel with its US healthcare panel to improve access to difficult-to-reach specialists. These include allied health professionals, such as dentists, NPs, PAs and surgical groups, a source told MM&M.

Knowledge Networks will also be fully integrated into GfK’s custom research and media activities in the US. An email sent to clients said that Simon Kooyman, CEO of Knowledge Networks, will become chief operations officer of GfK Custom Research North America.

GfK Group CEO Matthias Hartmann called Knowledge Networks “an important complement” to his firm’s US businesses, adding that the acquisition “presents a unique opportunity for GfK to better help clients meet their business objectives with richer insights.”

“The Knowledge Networks team is simply delighted to join GfK,” said Kooyman in a statement.

Knowledge Networks, which was backed by venture investors Oak Investment Partners, Alloy Ventures and Maveron, is expected to generate 2011 sales of about $58 million. The company has offices in New York, Washington DC, New Jersey, Massachusetts, Ohio, Illinois and California.