After its train wreck of manufacturing problems, Genzyme (Nasdaq: GENZ) seems like it's getting the cars back on track. The company recorded adjusted earnings of $0.42 per share in the third quarter. Not bad, although it fell well short of what analysts were hoping for from the company.

Patients in the U.S. are now getting full supplies of Cerezyme, and international demand is expected to be met before the end of the year. Fabrazyme should be fully stocked during the first half of next year. Genzyme is on track to meet the deadlines set by the Food and Drug Administration's consent decree, including moving the filling step to services contracted from Hospira (NYSE: HSP).

But I still wouldn't buy.

The problem, as I see it, is that the upside doesn't justify the potential downside, especially when trying to figure out whether sanofi-aventis (NYSE: SNY) is going to raise its $69-per-share offer. What's Sanofi going to be willing to pay -- $75, maybe $80 per share? That's 4% to 11% higher than where shares are now.

But what happens if Sanofi walks away? Pfizer (NYSE: PFE) just bought King Pharmaceuticals (NYSE: KG), so it's probably out as an acquirer. GlaxoSmithKline (NYSE: GSK) and Johnson & Johnson (NYSE: JNJ) have been rumored to be casually interested, but are they really going to offer much more than $69 if Sanofi walks away?

That leaves what investors would be willing to pay for Genzyme's shares. Before Sanofi came in, that was about $54 per share. Surely Genzyme is worth more having proven that it's getting back on track. But one quarter doesn't make a turnaround, and the downside is still substantial if Sanofi pulls its offer.

Proceed with caution, Fools. I'll be watching this drama from the comfort of my living room sofa.

Interested in keeping track of Genzyme as it makes its comeback and fends off Sanofi's lowball bid? Click here to add it to My Watchlist, which will help you keep track of all our Foolish analysis on Genzyme.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of GlaxoSmithKline and Johnson & Johnson and has a disclosure policy.