Index: MsgDefs.h
===================================================================
diff -u -rb2e6bfb639ed0bea5f7494eac096ce0316fc0342 -r1e879d0eb4a72396680e198d8b77393ca0e06921
--- MsgDefs.h	(.../MsgDefs.h)	(revision b2e6bfb639ed0bea5f7494eac096ce0316fc0342)
+++ MsgDefs.h	(.../MsgDefs.h)	(revision 1e879d0eb4a72396680e198d8b77393ca0e06921)
@@ -312,6 +312,10 @@
     MSG_ID_TD_SYRINGE_PUMP_FORCE_SENSOR_CALIBRATION_REQUEST = 0x8060,               ///< TD set syringe pump force sensor DAC calibration request
     MSG_ID_TD_GET_ALARM_PROPERTIES_REQUEST = 0x8061,                                ///< TD send alarm table properties request
     MSG_ID_TD_ALARM_PROPERTIES_RESPONSE = 0x8062,                                   ///< TD send alarm table properties response to Dialin
+    MSG_ID_TD_HDF_START_STOP_OVERRIDE_REQUEST = 0x8063,
+    MSG_ID_TD_HDF_CURRENT_RATE_OVERRIDE_REQUEST = 0x8064,
+    MSG_ID_TD_HDF_TARGET_TMP_OVERRIDE_REQUEST = 0x8065,
+    MSG_ID_TD_HDF_PUBLISH_INTERVAL_OVERRIDE_REQUEST = 0x8066,
 
     MSG_ID_FIRST_DD_TESTER_MESSAGE = 0xA000,                                            ///< First DD test message ID
     MSG_ID_DD_TESTER_LOGIN_REQUEST = MSG_ID_FIRST_DD_TESTER_MESSAGE,                    ///< DD tester log-in
Index: TDDefs.h
===================================================================
diff -u -rcb36235b4b58396a6bd8e51bf5c65475a4fd50c3 -r1e879d0eb4a72396680e198d8b77393ca0e06921
--- TDDefs.h	(.../TDDefs.h)	(revision cb36235b4b58396a6bd8e51bf5c65475a4fd50c3)
+++ TDDefs.h	(.../TDDefs.h)	(revision 1e879d0eb4a72396680e198d8b77393ca0e06921)
@@ -351,6 +351,7 @@
     TREATMENT_ISO_UF_STATE,                 ///< Isolated ultrafiltration.  No dialysate flow.  Ultrafiltration only.
     TREATMENT_SALINE_BOLUS_STATE,           ///< Deliver a saline bolus.  Blood pump draws from saline bag.  Dialyzer bypassed.
     TREATMENT_DIALYSATE_PAUSED_STATE,       ///< No dialysate flow.  Dialyzer bypassed.
+    TREATMENT_HDF_STATE,                    ///< Perform HDF. Deliver UF as prescribed.
     NUM_OF_TREATMENT_STATES                 ///< Number of treatment states (sub-modes)
 };
 typedef enum Treatment_States TREATMENT_STATE_T;    ///< Type for treatment states enumeration
@@ -442,6 +443,17 @@
 };
 typedef enum UF_Adjustments UF_ADJ_T;                   ///< Type for UF adjustments IDs enumeration
 
+/// Enumeration of HDF sub-mode states.
+enum HDF_States
+{
+    HDF_UF_STATE = 0,                                   ///< Ultrafiltration state of the HDF sub-mode state machine
+    HDF_UF_PAUSED_STATE,                                ///< Ultrafiltration Paused state of the HDF sub-mode state machine
+    HDF_UF_FLUID_BOLUS_STATE,                           ///< Fluid Bolus state of the HDF sub-mode state machine
+    NUM_OF_HDF_STATES                                   ///< Number of HDF sub-mode states
+};
+typedef enum HDF_States HDF_STATE_T;                    ///< Type for HDF states enumeration
+
+
 /**@}*/
 
 /**