Comparing two spreadsheets

Hi I have a problem comparing two spreadsheets of data/names.

The problem:

I have two lists with account names and numbers in coulumns A and B on sheet 1 and 2
Sheet 1 and 2 differ from each other in contents as well as number of accounts.

Is it possible to compare the two sheets and show duplicate entries in a 3rd sheet??? (blanck sheet).
In addition the two lists have a huge amount of data which make comparing in the same sheet difficult.......

Have tried various formulas but have not yet succeded

Hope that some of you can help