Exclude category from drop down list form

Question

I need a bit of quick help. How do I exclude category ID number 50 for example in drop down list form in Wordpress?

I have this code and I need to just insert the excluded category id.

<?php
$cate_id = retrieve_cat_data(true);
$cate_name = retrieve_cat_data(false);
for ($i = 0; $i < count($cate_name); $i++ ) { 
?>

<option value="<?php echo $cate_id[$i]; ?>"><?php echo $cate_name[$i]; ?>
</option><?php } ?>

Thanks in advance to everyone :)