LabCorp (NYSE:LH) is set to acquire toxicology testing company Medtox Scientific (Nasdaq: MTOX) for $241 million as the laboratory testing and diagnostics firm builds out its specialty testing offerings.

The definitive merger agreement calls for LabCorp to acquire Medtox for $27 per share in cash. That represents a 37 percent premium over Medtox’s $19.70 closing price on Friday. Medtox’s board of directors has already unanimously approved the agreement and recommended shareholder approval. Medtox, based in St. Paul, Minnesota, makes and sells diagnostic drug-screening devices.

LabCorp has made a concerted effort to grow by acquisition with a particular emphasis on specialty testing. Such tests include tests for infectious diseases, endocrinology, genetics, oncology and clinical trials. Through the end of 2011, LabCorp had invested more than $1.5 billion in acquisitions over the last three years, according to the company’s annual report. Two of those deals that fit the specialty testing growth strategy were last year’s deal to acquire DNA testing services firm Orchid Cellmark for $85 million and the 2010 acquisition of Genzyme Genetics for $925.2 million.

Medtox generated $108 million in 2011 revenue, according to its annual report. The company operates two business segments, laboratory services and diagnostics, representing 79 percent and 21 percent of 2011 revenue respectively.

Medtox does have operations located in close geographic proximity to LabCorp. The company’s diagnostic division is based in Burlington, , where LabCorp’s headquarters is also based.

Medtox’s North Carolina site is also registered by the U.S. Drug Enforcement Administration to make and distribute controlled substances, and to conduct research on controlled substances.

The acquisition is subject to customary closing conditions and approval by Medtox shareholders. The deal is expected to close in the third quarter.

(Read more about the latest deal here.)