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Thanks to all for the many helpful responses. The overwhelming consensus was
that food products made in the US that contain maltodextrin are GF.
Maltodextrin in vitamins and pills may not be GF. Also, maltodextrins from
non-US sources may not be GF.

An article in the latest "Gluten Free Living" was frequently cited for this
opinion. On the other hand, one person said that maltodextrin could be made
from barley, hence not GF.

It was mentioned that dextrins, frequently found in the same sorts of
products that contain maltodextrin, may not be GF.

For me, it would help if I were a chemist, so I knew what these things were!
Michael