PPD, which earlier this month agreed to be bought by two private equity firms, has entered into a confidentiality agreement with another suitor, the company wrote in a regulatory filing today.
PPD has until the end of the day on Nov. 1 to solicit rival bids.
As of Thursday, the company that entered into the confidentiality agreement had not submitted a formal bid.
The Carlyle Group and Hellman & Friedman are paying $33.25 per share for Wilmington-based PPD, a 30 percent premium over where the company's shares closed on the last day of trading before the deal was announced.
PPD's board has instructed Morgan Stanley to conduct a "go-show" process during which the investment bank contacted 22 parties to see if they were interested in making a superior offer to buy the company.
The parties included rivals who had earlier expressed interest in PPD.
To date, only the one party has responded.
PPD shares were trading at about $33 this afternoon.
PPD is part of a group of companies active in the Triangle, along with Quintiles and INC Research, that are known as contract research organizations.
CROs help pharmaceutical and biotechnology companies research, test and market new medicines.
PPD has about 1,400 workers in the Triangle.