Sigma-Aldrich Corp., a St. Louis-based life science and high technology company, plans to pay $350 million in cash to buy biopharmaceutical testing services provider BioReliance Holdings Inc. from Avista Capital Partners.

BioReliance, founded in 1947 and based in Rockville, Md., provides biologic testing, toxicology and animal health services for the pharmaceutical and biopharmaceutical industries. The contract research organization conducts tests to assess the safety of new products, but does not manage clinical trials of drugs on humans.

The acquisition would combine Sigma-Aldrich -- a growing company whose core strength lies in manufacturing -- with a much smaller, service-oriented firm.

Sigma, which reported revenue in 2010 of $2.1 billion, has 7,700 employees and offices in 40 different countries. The company develops, makes and distributes biochemical and organic chemical products and kits used in scientific research, including genomic and proteomic research.

BioReliance had about $110 million in revenues in 2010, and had forecast higher revenues in 2011. The company has laboratories in Rockville and Scotland, and offices in Japan and India. It employs more than 650 people.

Richter said that Sigma plans to maintain BioReliance's operations in the same locations and also to maintain "almost all" of its workforce.

Sigma-Aldrich, a publicly traded company, is banking that the acquisition will extend its reach into the promising new market of biologic drugs. 

Sigma's president and chief executive, Rakesh Sachdev, said the acquisition "enables us to support customers' needs to determine the quality and integrity of biological drugs at every step of the development and manufacturing process."

The combination "creates one of the broadest product and service offerings for the development and manufacture of biological drugs," BioReliance's president and chief executive Charles Harwood said in a written statement.

At least one securities expert was lukewarm about the deal. Dmitry Silversteyn, an analyst at Longbow Research in Independence, Ohio, described BioReliance as a company "with a checkered past ... that has gone through a lot of travails" and operates in a tough industry segment.

Sigma and BioReliance are "completely different businesses and business models. It will definitely be a learning experience for Sigma. It gives them another reason to call on their customers," Silversteyn said. "Perhaps it will expand their toolbox over time."

He said that BioReliance was acquired in 2004 by Invitrogen, which later became Life Technologies, for about $500 million. In 2007, Avista Capital Parners became the majority owner of BioReliance Holdings, acquiring the firm for about $210 million and installing a new executive chairman. Avista is a private equity firm with more than $4 billion under management.

Sigma's acquisition, which is subject to regulatory approval, is expected to close in the first quarter of 2012. The price of Sigma's common stock closed Monday at $61.85 a share, down 49 cents.