why does my $string print in duplicate?

Hi Can anyone shed some light on this small problem gor me. I have a list of email addresses from a mysql result. The email is sent from the script, and then the list of addresses is sent to the browser as a courtesy to the user. I remember reading in a PHP text book that you had to do something to stop all the data appearing twice, but can not find the information now that I need it. Why do all the email addresses appear in duplicate and how can I stop it? Many thanks for any help Jim