Index: wp-includes/link-template.php
===================================================================
--- wp-includes/link-template.php	(revision 5346)
+++ wp-includes/link-template.php	(working copy)
@@ -438,7 +438,7 @@
 		return;
 
 	$title = apply_filters('the_title', $post->post_title, $post);
-	$string = '<a href="'.get_permalink($post->ID).'">';
+	$string = '<a href="'.get_permalink($post->ID).'" rel="prev">';
 	$link = str_replace('%title', $title, $link);
 	$link = $pre . $string . $link . '</a>';
 
@@ -454,7 +454,7 @@
 		return;
 
 	$title = apply_filters('the_title', $post->post_title, $post);
-	$string = '<a href="'.get_permalink($post->ID).'">';
+	$string = '<a href="'.get_permalink($post->ID).'" rel="next">';
 	$link = str_replace('%title', $title, $link);
 	$link = $string . $link . '</a>';
 	$format = str_replace('%link', $link, $format);