You could load the concatenation of each pair of the existing values into a
collection, then go through the new data, and try to add the concatenated
values to the collection. If you get an error, that row already exists. If
not, then copy the data to the bottom of an existing sheet.

You can see an example of using a collection to get a unique list at John
Walkenbach's site.
http://www.j-walk.com/ss/excel/tips/tip47.htm

You should be able to adapt that to your situation.

--
Regards,
Tom Ogilvy


"John_Carty" wrote in message
...
I have a worksheet that contains two columns of data, I need a macro that
will write unique values from the source worksheet to an existing
worksheet.
The value is only considered to be unique if the combination of the two
values does not already exist in the target worksheet. The macro should
run
each time the worksheet is opened.

Any help is much appreciated.

Regards,

John