Create a custom formula for data validation

I would like to create a formula that I can input into a custom data validation that will not allow duplicate enteries and will only allow the data being entered to be from a named list. I know I can use the custom formula =COUNTIF($A$1:$A$500,A16)=1 with not allowing duplicates. But I'm not sure how, or if I can, also have a formula that at the same time does not allow items to be entered that are not on a named list. Any ideas would be appreciated. Thanks!

Hi barber,

Use the AND function... =AND(condition1,condition2,...)

=AND(COUNTIF($A$1:$A$500,A16)=1,NOT(ISNA(VLOOKUP(A16,table,1,0))))

Of course, you can change the the second condition to your own formula...

That did the trick! Thank you so much.