diff --git a/wp-admin/options-discussion.php b/wp-admin/options-discussion.php
index e45ff4bd99..5f0b686919 100644
--- a/wp-admin/options-discussion.php
+++ b/wp-admin/options-discussion.php
@@ -57,7 +57,7 @@ if ($action == 'retrospam') {
 	<h2><?php _e('Discussion Options') ?></h2> 
 	<form name="form1" method="post" action="options.php"> 
 		<input type="hidden" name="action" value="update" /> 
-		<input type="hidden" name="page_options" value="'default_pingback_flag','default_ping_status','default_comment_status','comments_notify','moderation_notify','comment_moderation','require_name_email','comment_max_links','moderation_keys'" /> 
+		<input type="hidden" name="page_options" value="'default_pingback_flag','default_ping_status','default_comment_status','comments_notify','moderation_notify','comment_moderation','require_name_email','comment_whitelist','comment_max_links','moderation_keys'" /> 
 <fieldset class="options">
         <legend><?php _e('Usual settings for an article: <em>(These settings may be overridden for individual articles.)</em>') ?></legend> 
 		<ul> 
@@ -101,11 +101,8 @@ if ($action == 'retrospam') {
 				<input name="comment_moderation" type="checkbox" id="comment_moderation" value="1" <?php checked('1', get_settings('comment_moderation')); ?> /> 
 				<?php _e('An administrator must approve the comment (regardless of any matches below)') ?> </label> 
 			</li> 
-			<li> 
-				<label for="require_name_email"> 
-				<input type="checkbox" name="require_name_email" id="require_name_email" value="1" <?php checked('1', get_settings('require_name_email')); ?> /> 
-				<?php _e('User must fill out name and e-mail') ?> </label> 
-			</li> 
+			<li><label for="require_name_email"><input type="checkbox" name="require_name_email" id="require_name_email" value="1" <?php checked('1', get_settings('require_name_email')); ?> /> <?php _e('Comment author must fill out name and e-mail') ?></label></li> 
+			<li><label for="comment_whitelist"><input type="checkbox" name="comment_whitelist" id="comment_whitelist" value="1" <?php checked('1', get_settings('comment_whitelist')); ?> /> <?php _e('Comment author must have a previously approved comment') ?></label></li> 
 		</ul> 
 </fieldset>
 <fieldset class="options">
diff --git a/wp-admin/upgrade-schema.php b/wp-admin/upgrade-schema.php
index 06891a6a04..45e20a192f 100644
--- a/wp-admin/upgrade-schema.php
+++ b/wp-admin/upgrade-schema.php
@@ -211,6 +211,7 @@ function populate_options() {
 	add_option('use_linksupdate', 0);
 	add_option('template', 'default');
 	add_option('stylesheet', 'default');
+	add_option('comment_whitelist', 0);
 
 	// Delete unused options
 	$unusedoptions = array ('blodotgsping_url', 'bodyterminator', 'emailtestonly', 'phoneemail_separator', 'smilies_directory', 'subjectprefix', 'use_bbcode', 'use_blodotgsping', 'use_phoneemail', 'use_quicktags', 'use_weblogsping', 'weblogs_cache_file', 'use_preview', 'use_htmltrans', 'smilies_directory', 'rss_language', 'fileupload_allowedusers', 'use_phoneemail', 'default_post_status', 'default_post_category', 'archive_mode', 'time_difference', 'links_minadminlevel', 'links_use_adminlevels', 'links_rating_type', 'links_rating_char', 'links_rating_ignore_zero', 'links_rating_single_image', 'links_rating_image0', 'links_rating_image1', 'links_rating_image2', 'links_rating_image3', 'links_rating_image4', 'links_rating_image5', 'links_rating_image6', 'links_rating_image7', 'links_rating_image8', 'links_rating_image9', 'weblogs_cacheminutes', 'comment_allowed_tags', 'search_engine_friendly_urls', 'default_geourl_lat', 'default_geourl_lon', 'use_default_geourl');
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 09dfb4b89a..70c0254e13 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1473,13 +1473,26 @@ function get_posts($args) {
 }
 
 function check_comment($author, $email, $url, $comment, $user_ip) {
+	global $wpdb;
+
 	if (1 == get_settings('comment_moderation')) return false; // If moderation is set to manual
 
 	if ( (count(explode('http:', $comment)) - 1) >= get_settings('comment_max_links') )
 		return false; // Check # of external links
 
-	if ('' == trim( get_settings('moderation_keys') ) ) return true; // If moderation keys are empty
-	$words = explode("\n", get_settings('moderation_keys') );
+	// Comment whitelisting:
+	if ( 1 == get_settings('comment_whitelist')) {
+		$ok_to_comment = $wpdb->get_var("SELECT comment_approved FROM $wpdb->comments WHERE comment_author_email = '$email' and comment_approved = '1' ");
+		if ( 1 == $ok_to_comment && false === strpos( $email, get_settings('moderation_keys')) )
+			return true
+	return false;
+	}
+
+	$mod_keys = trim( get_settings('moderation_keys') );
+	if ('' == $mod_keys )
+		return true; // If moderation keys are empty
+	$words = explode("\n", $mod_keys );
+
 	foreach ($words as $word) {
 		$word = trim($word);