Amazon.com, eBay’s main rival in online shopping, invested in Bill Me Later last year and has integrated the payment service into its site. It is unclear whether that relationship will continue. Amazon declined to comment on the transaction.

Shares of eBay fell on Monday along with the overall market, dropping $1.05, or 5.5 percent, to $17.89. Although eBay’s stock is at a five-year low, Mr. Donahoe said the company’s strong balance sheet and cash balance have allowed it to take advantage of Bill Me Later’s declining value in a market that has been rough on all companies in the finance sector.

“We feel a little like Warren Buffett. We are a strong company, and at times like this we can move to take advantage of the market environment,” he said in an interview.

EBay also announced on Monday that it was acquiring the popular Danish classified advertising site DBA.dk and the automotive marketplace BilBasen.dk for $390 million, from the Danish media mogul Karsten Ree. The deal is one of the largest in Denmark’s history. A local newspaper reported that the companies had negotiated on and off for four years.

EBay has been steadily building or buying classified Web sites and already owns properties like Kijiji, Gumtree, Marktplaats, LoQuo and mobile.de. EBay also owns a 25 percent stake in the American online classifieds leader Craigslist, but its interest in buying the firm outright led the companies to sue each other this year.

EBay’s attempt to stitch together a global network of classified advertising sites is partly intended to create an alternative to its sagging traditional business of auctions. For the first time on Monday, eBay disclosed some financial information about its classifieds holdings, saying they generated $260 million in revenue last year  which it described as three to four times the estimated annual revenue of the closely held Craigslist.