How to delete completely duplicate rows

Hi,
 
I want to delete duplicates in my table. I've dropped the unique constraint to insert my data.
My id value is a hash calculated witch the values of the two other columns.
So I want to delete all columns, which are indentical, but keeping one.
 
DELETE FROM table t1 USING table t2 WHERE t1.id = t2.id AND t1.ctid > t2.ctid

But the oids aren't unique enough.
What else could I do?

Janek