diff --git a/ex-5_14-19.scm b/ex-5_14-19.scm
index e4b9931..9077ec3 100644
--- a/ex-5_14-19.scm
+++ b/ex-5_14-19.scm
@@ -74,4 +74,27 @@
 
 (display "\nex-5.19 - breakpoint\n")
 
+(define (set-breakpoint machine label n)
+  ((machine 'set-breakpoint) label n))
+
+(define (cancel-breakpoint machine label n)
+  ((machine 'cancel-breakpoint) label n))
+
+(define (proceed machine)
+  (machine 'proceed))
+
+(set-register-contents! factorial-machine 'n 6)
+(set-register-contents! factorial-machine 'val 0)
+
+(set-breakpoint factorial-machine 'fact-loop 1)
+(start factorial-machine)
+
+(assert (get-register-contents factorial-machine 'n) 6)
+(proceed factorial-machine)
+(assert (get-register-contents factorial-machine 'n) 5)
+(proceed factorial-machine)
+(cancel-breakpoint factorial-machine 'fact-loop 1)
+(assert (get-register-contents factorial-machine 'n) 4)
+(proceed factorial-machine)
+(assert (get-register-contents factorial-machine 'val) 720)
 
diff --git a/misc/sicp-regsim.scm b/misc/sicp-regsim.scm
index d32c690..f3322fc 100644
--- a/misc/sicp-regsim.scm
+++ b/misc/sicp-regsim.scm
@@ -121,6 +121,9 @@
         (stack (make-stack))
         (instruction-count 0)
         (instruction-trace #f)
+        (breakpoints '())
+        (location (list 'none 0))
+        (proceed #f)
         (the-instruction-sequence '()))
     (let ((the-ops
            (list (list 'initialize-stack
@@ -143,19 +146,32 @@
           (if val
               (cadr val)
               (error "Unknown register:" name))))
+      (define (update-location inst-text)
+        (if (eq? (car inst-text) 'label)
+          (set! location (list (cadr inst-text) 0))
+          (set-cdr! location (list (+ (cadr location) 1)))))
       (define (execute)
         (let ((insts (get-contents pc)))
           (if (null? insts)
               'done
               (begin
-                ((instruction-execution-proc (car insts)))
-                (if instruction-trace
+                (update-location (instruction-text (car insts)))
+                (if (and (member location breakpoints)
+                         (not proceed))
                   (begin
+                    (display "stopped @ ")
                     (display (instruction-text (car insts)))
-                    (newline)))
-                (if (not (eq? 'label (car (instruction-text (car insts)))))
-                  (set! instruction-count (+ instruction-count 1)))
-                (execute)))))
+                    (newline))
+                  (begin
+                    (set! proceed #f)
+                    ((instruction-execution-proc (car insts)))
+                    (if instruction-trace
+                      (begin
+                        (display (instruction-text (car insts)))
+                        (newline)))
+                    (if (not (eq? 'label (car (instruction-text (car insts)))))
+                      (set! instruction-count (+ instruction-count 1)))
+                    (execute)))))))
       (define (dispatch message)
         (cond ((eq? message 'start)
                (set-contents! pc the-instruction-sequence)
@@ -175,6 +191,13 @@
               ((eq? message 'get-register) lookup-register)
               ((eq? message 'install-operations)
                (lambda (ops) (set! the-ops (append the-ops ops))))
+              ((eq? message 'set-breakpoint)
+               (lambda (label count) (set! breakpoints (cons (list label count) breakpoints))))
+              ((eq? message 'cancel-breakpoint)
+               (lambda (label count) (set! breakpoints (delete (list label count) breakpoints))))
+              ((eq? message 'proceed)
+               (set! proceed #t) (execute))
+              ((eq? message 'cancel-all-breakpoints) (set! breakpoints '()))
               ((eq? message 'stack) stack)
               ((eq? message 'operations) the-ops)
               (else (error "Unknown request -- MACHINE" message))))
@@ -207,10 +230,12 @@
        (lambda (insts labels)
          (let ((next-inst (car text)))
            (if (symbol? next-inst)
-               (receive (cons (make-instruction (list 'label next-inst)) insts)
+             (begin
+               (set! insts (cons (make-instruction (list 'label next-inst)) insts))
+               (receive insts
                         (cons (make-label-entry next-inst
                                                 insts)
-                              labels))
+                              labels)))
                (receive (cons (make-instruction next-inst)
                               insts)
                         labels)))))))