Quintiles’ (NYSE:Q) initial public stock offering is turning into a payday for certain shareholders in the largest biopharmaceutical services company in the world.

Insiders to the Durham company – executives, directors and officers – sold more 510,140 Quintiles shares in the last week. Besides outgoing President and Chief Operating Officer John Ratliff, who sold 9 million shares at $42.55 per share to net just over $9 million,  another executive, Chief Customer and Governance Officer Derek Winstanly, sold 90,000 shares for $43.03 per share in a transaction valued $3.8 million, according to securities filings.

And Michael Mortimer, executive vice president and chief administration officer, sold 200,000 shares at the price of $42.55 per share, enough to pocket $8.5 million, filings show.

Michael J. Evanisko, a member of Quintiles’ board of directors, sold 8,000 shares in two transactions, both sales for the $43 per share price. Evanisko’s sales brought him $344,000.

At the average price of $42.64 per share, those insider sales were valued at more than $21.7 million.

But Quintiles executives aren’t the only ones pocketing money by selling Quintiles stock. The private equity firms that invested in Quintiles are also taking some money off of the table.

Private equity firm TPG, which gained its equity stake in Quintiles in 2008 when it was one of the firms that bought out the shares owned by One Equity Partners, sold more than 1 million shares at $42.37 per share in a Nov. 22 transaction valued at $42.9 million, according to filings. Even after the sale, TPG still owns more than 21.4 million shares in Quintiles.

Another private equity investor, 3I Corp., sold 712,126 Quintiles shares on Nov. 20, a transaction valued at more than $30.1 million. After the sale, 3I still owns 15.1 million Quintiles shares, filings show

There’s a reason that these stock sales are happening now. The lock-up period, the time after an IPO during which insiders stock option owners are barred from cashing out their stakes, expired on Nov. 17.

The purpose of a lockup is to prevent a mass dumping of shares that could push down a company’s stock price. As the lockup expiration approached, CEO Tom Pike prepared the investment community for the coming stock sales that would follow.

“We expect there will be interest on the part of existing and former employee shareholders and vested stock option holders, some of whom have held shares for a decade, to take advantage of this liquidity and diversification opportunity, particularly due to the company’s long tenure as a private company,” Pike said during the company’s conference call last month to discuss third quarter financial results.

To offset the effects that the sale of the unlocked shares, Quintiles announced a stock buyback program, authorized by the company’s board of directors, to repurchase up to $125 million in stock or stock options. Pike said at that time that money for the stock repurchases would come from Quintiles’s cash holdings. As of Sept. 30, Quintiles balance sheet showed $609.7 million in cash and cash equivalents.