Hi,
Assuming your large list is A1:A21
Assuming your small list starts in B1, going down the column

Select all items in the small list, starting with B1
Open the Conditional Format dialog box
Select 'Formula is'
Put this in the formula field:
=COUNTIF($A$1:$A$21,$B1)=0
Select your format (eg red bold font)
OK
The cells you want should be red bold font.

Change the references to suit your data.
Hope this is what you need.
Regards - Dave.