check row before insert

Hi,

I have a table as follows:

protein_id | name
___________ ______

P04667 Albumin
P45366 Lactoglobulin
....
etc

I have a perl script that will insert data into this table from a file
containing a list of protein_id and names. However, I only want to insert
proteins where they are not already preset in the database. Is there a way to
do this using an SQL command?

Thanks