Log on to www.google.com and type in "yellow tongue". I'm not sure I've ever
hear the word "tonge".

Among the "hits" was

http://www.wrongdiagnosis.com/sym/tongue_symptoms.htm

Could someone tell me some of the possible causes for a "yellow tonge"?
The back half of my tonge has this yellow goop the last few days that
wont go away no matter how much i brush & rinse etc. Also I have a
metalic/sour taste. I have a doctor's appointment next week but maybe
someone can set my mind at ease?

tia 08/02

It's probably due to a change in the bacterial flora in your mouth.  If the
changes just happened in the last few days, it's probably nothing to worry
about and may clear up on its own.  Are you taking antibiotics now or
recently -- that could be a reason.  Have you made any major/significant
changes in your diet recently?  Using a different toothpaste?  It's
impossible to tell without seeing you, but even seeing you it often is hard
to pinpoint the cause.  Good luck!