Voilà mon code:
<tr>
<td><input name="Annuler" type="reset" value="Annuler"></td>
<td><input name="Su" type="submit" value="Supprimer"></td>
</tr>
</table>
</form>
<?php
mysql_connect("localhost","root","")or die("impossible de vous connecter");
mysql_select_db("bne_bd")or die ("Impossible de selection cette Base");
if(isset($_POST['Su'])){
$Mat=$_POST["Agent"];
$sql="DELETE FROM agent WHERE Mat_agent=".$Mat."";
mysql_query($sql) or die ( mysql_error());
echo("agent bien supprimé");}
?>