Just how much value have startups lost since the economy took a nosedive in September 2008? Ask Amazon (NSDQ: AMZN), which often takes stakes in private companies. The value of its investments in private companies plummeted 64 percent from September 30, 2008 to March 31, 2009, according to the company’s 10-Q filed this morning.  According to the SEC filing, the value of Amazon’s private-company investments dropped to $89 million by the end of Q109 from $248 million at the end of Q308. To be sure, the company sold its stake in Bill Me Later when it was bought by eBay (NSDQ: EBAY) in October 2008, but it held only a small stake in the company and assuming that stake was around 5 percent, the company’s private investments still lost over 50 percent of their value during the same period.

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Amazon is active in the private investment space.  A few weeks ago it made a seed investment in BookTour, an online directory of author events, and it also took a stake recently in ad optimization firm Yieldex.  It also holds a stake in shopping site The Talk Market.

For a little context, while this is certainly a large drop, the Dow Jones (NYSE: NWS) Index fell 41 percent during the same period.  Since private company valuations tend to be more volatile than public company valuations on a relative basis, the decline may not be as jarring.  Still, tell that to Amazon which is currently holding a fraction of its original investments’ value.