Research Triangle Park, N.C. — Durham-based Quintiles announced Friday it has filed federal paperwork for an initial public offering of common stock.

The world’s largest life science services firm, headquartered at Research Triangle Park, went private in 2008. Rumors surfaced months ago that Quintiles was planning to return to the stock market, but the company repeatedly declined to comment about its financial plans.

The firm said Friday that the number of shares and price range of the initial offering have not yet been determined. Quintiles plans to use some of the money raised in the sale to repay long-term debt. Reuters news service reported the company could raise up to $600 million in the IPO.

The firm reported some $3.5 billion in revenue for 12 months, ending June 30 of 2012, according to Moody's Investors Service.
The company was taken private by co-founder and top executive Dennis Gillings in 2008. Gillings, then the chairman and chief executive officer, cited being free from the scrutiny given public companies as one of the major reasons for the decision.

A group of private-equity firms led by TPG and Bain bought Quintiles in 2008 in a deal that valued the company at about $3.8 billion, according to sources.