OK, I'm in a bit of a pickle. I am in the process of decorating cookies and using antonia's royal. Long story short....ran out of meringue powder, can I sub powdered egg whites for this??? Thanks in advance to all who reply!

Eeeeek. I actually don't know the answer to this but I'll give you a bump to the top.

I would think so, I live in the Uk so don't have meringue powder as such. I use merriwhite which is powdered egg white substitute and it works really well. HTH

Meringue powder contains powdered egg white, but it also has cream of tartar for stability and some corn starch for thickening.
According to Cook's Thesaurus, the two can be used interchangeably: http://www.foodsubs.com/Eggs.html#powdered%20egg%20white

Yes, you can use 5 or 6 large egg whites in lieu of the meringue powder and 1st addition of water.

Thank you everyone!!!