When a string is entered in file1.xls column range A:A, I would like to see if it is on file2.xls column range A:A and if it is, a message box come up with instructions...and to deny the entry of the string. Of course, if it is not in file2.xls, then the string will remain.

file1.xls (A:A) file2.xls (A:A)

BobA TimE
JackC
SaraE


If I try to enter TimE into file1.xls, a message will pop up because TimE is listed in file2.xls


ANY help would be appreciated. Thanks in advance.