He said Amazon had temporarily sold out of hard copies of "What Happened: Inside the Bush White House and Washington's Culture of Deception," the new tell-all book by former White House press secretary Scott McClellan.
It's still available, however, for electronic downloading, Bezos said.
"That's one of the great things about electronic books," he said. "They don't go out of stock."
Bezos has said Kindle e-books now account for 6 percent of sales among the 125,000 titles available on the site in both electronic and print formats. The company did not elaborate on that figure.
The online retailer cut the Kindle's price by $40 to $359 on Tuesday but still won't say how many have sold. The company also refuses to divulge the total number of e-books it has sold.
Kindle launched last November and sold out in hours. Amazon sorted out its supply chain and manufacturing problems, and the device was back on sale in April.
Despite the price cut, the Kindle still costs more than Sony Corp.'s competing Reader, which retails for $299.
