text: i want to avoid duplication value in excel colum? i want to avoide duplication value in on column/it must show error/wornning that value aready exits. o caçador has apoint, but it will work for the 50 rows only change the references in that formula of $a$50 into $a50. this will causes countif to enter all cells from a1 to the cell above me.  or you can use my way (which is also based on countif function) i used to add a column column b) with this formula =countif( a4, $a$1:a4) and change its conditional formatting into red when is more than zero. in this example, the cell will be colored in red when you entered a value that is saved above, no matter where you copy and paste it.  enjoy my profile, i am the vbaxlman