When I type =SUM and then press Ctrl-Shift-A excel shows me the field
names in the formulabar that I can then copy and use. Is there a way
to retrieve those fieldnames through VBA directly?

What are wanting to use those for? Those field names are just
variables that it needs. If go into your VBA code and type
"worksheetfunction.Sum( ", then the intellisense pops up and you'll
see all the arguments/variables that the Sum() function needs. Will
that do?

What are wanting to use those for? *

I need the fieldnames in runtime because I created my own function
dialog. The default excel function dialog is fine for most purposes
and I would like very much to use that as the basis for an extended
dialog, but I need more information to evaluate and break down complex
formulas. Also the Evaluate Tool in excel does not give me the
information I want.

Regards,
André

Maybe you could try making your own function in VBA code? Then you
would have access to those variables that are used in your own
function. Can you post some code of what you have so far maybe? I
guess I'm still not understanding exactly. sorry Those field names
are nothing but values ASSIGNED to them...