Duplicates over two lists

I have a list of approx. 5000 alphanumeric reference numbers, I have another list with 3500 of these that have been completed and would like to find a way to display the remaining 1500 uncompleted ones.

They have not been completed in order so I can't simply select the last 1500 of the original list.

I have read these forums and a couple of sites that seem to offer solutions but I can't get them to work....


I have tried to name the lists (insert>name>define)

Then produce a third list called "In1not2" and used the following array formula:

=IF(ISERROR(MATCH(List1,List2,0)),List1,"")

Although this worked on a small sample my excel crashes (not responding) every time i try it on the full list.


I have also tried with conditional formatting but to no avail

any help appreciated

HI
Paste the first list in col A and 2nd list in Col B and press the yellow button (See compare.zip). it will compare Col A with B and any missing ones will be listed in col C
Ravi