A TidBITS reader in France who wishes to remain anonymous has alerted us to a tempest brewing around older units of the Mac Pro line. Apparently, users noticed a strong smell emanating from the machines, particularly when they were new, and the French newspaper Liberation just published about the experiences of a lab researcher who reportedly analyzed the emissions and found volatile organic compounds, including , a known carcinogen.
AppleCare representatives in France contacted by our reader confirmed the problem as affecting Mac Pros built before 2008 but refused to put it in writing. Apple spokesman Bill Evans told, "We have not found anything that supports this claim, but continue to investigate it for the customer."
Apple's discussion forum contains posts from 2007 from users who experienced the smell, some of whom had their Macs replaced under AppleCare. In some cases, the smell may have been related to near the power supply,  on the access door, or  on the processor heat sinks. Many, though not all, of the affected Macs were built in China.
The (reportedly after having several previous attempts deleted by Apple) hasn't generated nearly the number of "me too" posts as the 2007 threads, although some Mac Pro users who haven't experienced the smell are expressing concern.
It's difficult to know what to suggest with regard to this issue. Strong smells coming from a computer aren't likely to be a good thing, although without careful analysis, it's impossible to know whether the compounds being emitted are actually toxic, and if they're being emitted in concentrations that could pose a health risk. Plus, the machines in question are nearly a year old at minimum, so if there was a manufacturing problem, Apple has undoubtedly addressed it months ago. There seems no reason to suspect current Mac Pro units, but if you have a pre-2008 Mac Pro that emits a strong smell, or did for some time when it was new, you may wish to contact Apple about it.