diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index ca0ff1838..6521143b6 100755
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2009-11-17  Eric Schulte  <schulte.eric@gmail.com>
+
+	* org-exp-blocks.el (org-export-blocks-format-ditaa): Use sha1
+	hash keys to cache and re-use images generated by the
+	org-exp-blocks interface to ditaa and dot.
+
 2009-11-17  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* org-html.el (org-export-as-html): Move the home/up link into
diff --git a/lisp/org-exp-blocks.el b/lisp/org-exp-blocks.el
index 71e1608f9..72fe6c492 100644
--- a/lisp/org-exp-blocks.el
+++ b/lisp/org-exp-blocks.el
@@ -217,9 +217,15 @@ Specify the path at which the image should be saved as the first
 element of headers, any additional elements of headers will be
 passed to the ditaa utility as command line arguments."
   (message "ditaa-formatting...")
-  (let ((out-file (if headers (car headers)))
-	(args (if (cdr headers) (mapconcat 'identity (cdr headers) " ")))
-	(data-file (make-temp-file "org-ditaa")))
+  (let* ((args (if (cdr headers) (mapconcat 'identity (cdr headers) " ")))
+         (data-file (make-temp-file "org-ditaa"))
+         (hash (sha1 (prin1-to-string (list body args))))
+         (raw-out-file (if headers (car headers)))
+         (out-file-parts (if (string-match "\\(.+\\)\\.\\([^\\.]+\\)$" raw-out-file)
+                             (cons (match-string 1 raw-out-file)
+                                   (match-string 2 raw-out-file))
+                           (cons raw-out-file "png")))
+         (out-file (concat (car out-file-parts) "_" hash "." (cdr out-file-parts))))
     (unless (file-exists-p org-ditaa-jar-path)
       (error (format "Could not find ditaa.jar at %s" org-ditaa-jar-path)))
     (setq body (if (string-match "^\\([^:\\|:[^ ]\\)" body)
@@ -229,9 +235,21 @@ passed to the ditaa utility as command line arguments."
 			    "\n")))
     (cond
      ((or htmlp latexp docbookp)
-      (with-temp-file data-file (insert body))
-      (message (concat "java -jar " org-ditaa-jar-path " " args " " data-file " " out-file))
-      (shell-command (concat "java -jar " org-ditaa-jar-path " " args " " data-file " " out-file))
+      (unless (file-exists-p out-file)
+        (mapc ;; remove old hashed versions of this file
+         (lambda (file)
+           (when (and (string-match (concat (regexp-quote (car out-file-parts))
+                                            "_\\([[:alnum:]]+\\)\\."
+                                            (regexp-quote (cdr out-file-parts)))
+                                    file)
+                      (= (length (match-string 1 out-file)) 40))
+             (delete-file (expand-file-name file
+                                            (file-name-directory out-file)))))
+         (directory-files (or (file-name-directory out-file)
+                              default-directory)))
+        (with-temp-file data-file (insert body))
+        (message (concat "java -jar " org-ditaa-jar-path " " args " " data-file " " out-file))
+        (shell-command (concat "java -jar " org-ditaa-jar-path " " args " " data-file " " out-file)))
       (format "\n[[file:%s]]\n" out-file))
      (t (concat
 	 "\n#+BEGIN_EXAMPLE\n"
@@ -259,14 +277,32 @@ digraph data_relationships {
 }
 #+end_dot"
   (message "dot-formatting...")
-  (let ((out-file (if headers (car headers)))
-	(args (if (cdr headers) (mapconcat 'identity (cdr headers) " ")))
-	(data-file (make-temp-file "org-ditaa")))
+  (let* ((args (if (cdr headers) (mapconcat 'identity (cdr headers) " ")))
+         (data-file (make-temp-file "org-ditaa"))
+         (hash (sha1 (prin1-to-string (list body args))))
+         (raw-out-file (if headers (car headers)))
+         (out-file-parts (if (string-match "\\(.+\\)\\.\\([^\\.]+\\)$" raw-out-file)
+                             (cons (match-string 1 raw-out-file)
+                                   (match-string 2 raw-out-file))
+                           (cons raw-out-file "png")))
+         (out-file (concat (car out-file-parts) "_" hash "." (cdr out-file-parts))))
     (cond
      ((or htmlp latexp docbookp)
-      (with-temp-file data-file (insert body))
-      (message (concat "dot " data-file " " args " -o " out-file))
-      (shell-command (concat "dot " data-file " " args " -o " out-file))
+      (unless (file-exists-p out-file)
+        (mapc ;; remove old hashed versions of this file
+         (lambda (file)
+           (when (and (string-match (concat (regexp-quote (car out-file-parts))
+                                            "_\\([[:alnum:]]+\\)\\."
+                                            (regexp-quote (cdr out-file-parts)))
+                                    file)
+                      (= (length (match-string 1 out-file)) 40))
+             (delete-file (expand-file-name file
+                                            (file-name-directory out-file)))))
+         (directory-files (or (file-name-directory out-file)
+                              default-directory)))
+        (with-temp-file data-file (insert body))
+        (message (concat "dot " data-file " " args " -o " out-file))
+        (shell-command (concat "dot " data-file " " args " -o " out-file)))
       (format "\n[[file:%s]]\n" out-file))
      (t (concat
 	 "\n#+BEGIN_EXAMPLE\n"