Cannot retrieve the data from a MS-SQLServer VARCHAR(n>255) or TEXT field

Help,

I cannot retrieve the data from a MS-SQLServer VARCHAR(n>255) or TEXT field
in my Delphi program. I've tried all combinations of
  MmoChangeLog.Text :=
  MmoChangeLog.Assign()
  MmoChangeLog.Lines.Add()
  MmoChangeLog.Lines.AddStrings()
left of the assignment, and
  Fields[0].AsVariant;
  Fields[0].AsString;
  Fields[0].VAlue;
  Fields[0].Text;
right of the assignment,
but nothing seems to work.
The data are retrieved with a query:
 SELECT MUT_DESCRIP FROM MUTSTRU WHERE MUT_ID=15

It almost looks like a FAQ, but so far I haven't found anything.
Who can help me out?

TIA
Jan Doggen