I have a sql statement which needs to be modified.  It combines several fields or any combination  may or may not be null.  I need one space between each value when it exists.  I was wondering if using case for this might be the best approach.

select action,quantity,
Ltrim((isnull(ACTION,'')+  ' '+ isnull(QUANTITY,'') + ' '+ isnull(UNITOFMEASURE,'') +
' ' + isnull(ROUTE,'') + ' ' + isnull(FREQUENCY,'') + ' ' + isnull(SYMPTOM,'') + ' ' + isnull(ADDITIONALSIGNETUR,''))) as sig

from medicationorder

No need.  Since concatenating a NULL to another string simply results in NULL, which you can then still use as the expression to test for the isnull function, you can simplify this whole thing like so...

select action,quantity,
Ltrim((isnull(ACTION+' ','') + isnull(QUANTITY+' ','') + ...