Conditional formatting - duplicate entries across 3 columns

Hi

I am having trouble working out a formula for finding duplicate data across 3 columns. At the moment I have this formula:

=countifs(A:A, A1, B:B, B1)>3

So when data in columns A and B duplicate more than 3 times they highlight red. I need it to include column C also but for some reason it doesn't seem to work. I thought by using this formula "=countifs(A:A, A1, B:B, B1, C:C, C1)>3" it would work but all it does it highlight cells in column A? My range is A1:C1000.

Thanks for your time!

Thanks Bernie! Thought it would be as simple as that. D'oh!

Cheers