Fortune 500 rank: 85
2009 profit: $12.9 billionWhat a difference an acquisition makes. Before buying Schering-Plough for $41 billion in 2009, Merck was facing patent losses, heavy competition, and a pipeline of drugs with bad chances for FDA approval.
Now with a revitalized pipeline, including treatments like Schering's Nasonex nasal spray, Merck is back on track. Earnings grew by more than half in 2009, driven mostly by a one-time gain it booked from the merger.
NEXT: 8. AT&T