$("#bbbb").change(function () {
$.ajax({
type: 'POST',
url:'ajax.php',
data: 'islem=1&id=50°er='+$("#bbbb").val()
});
});
<?php
$sql = mysql_query("SELECT * FROM tablom");
while ($list_deger = mysql_fetch_row($sql)) {
echo "<select name='aaaa' id='bbbb'>";
echo "<option value='$list_deger [0]'>$list_deger [1]</option>";
echo "</select>";
}
?>