DURHAM, N.C. (AP) — Clinical testing company Quintiles Transnational wants to become a public company again after nearly a decade in private hands.

The Durham, N.C.-based company said Friday it filed with the U.S. Securities and Exchange Commission for a proposed initial public offering of stock worth up to $600 million.

Quintiles calls itself the world's largest contract research company helping large pharmaceutical companies test and sell drugs.

The company founded in 1982 by biostatistics professor Dennis Gillings became a public company in 1994. Gillings and others bought out stockholders to take Quintiles private again in 2003. It's now owned by Gillings; hedge funds Bain Capital Partners and TPG Global; and Singapore state investment company Temasek Holdings.

Quintiles said its revenues last year were $3.7 billion.