Yes, MSG can cause hives. I know it from experience and I can provoke it by eating certain chinese foods or for instance sausage that has a lot of MSG.
On yahoo answers......
"You've got lots of good advice here and I just had to add mine because I suffer from hives-- diagnosed as 'ideopathic urticara'- for months at a time.
The best advice my dermatologist ever gave me: Don't scratch. When you scratch your cells burst and release histamines... you may find yourself swollen. I have had this condition to the point of being disfigured and in the ER being pumped full of steroids.
(don't let anyone prescribe steroids to stop your reaction unless it's life threatening, this could cause a rebound effect)
My advice: Don't drive yourself insane trying to find a cause to your hives. The immune system is a mystery.
Your doctor will help you find the right histamine blocker. All those anti-histamines out there block differently... you have to experiment until one works for you. In my case, it's Allegra-- you could also try Zyrtec or Claritin. (Those are the big three used to combat hives.)
Also, use a cool pack to keep the hotspots from drving you insane. Avoid hot showers, use a bath oil after bathing and PAT dry-- do NOT rub!"