We can use this function in two ways with run time settings in loadrunner and with lr_set_debug_message. Example 1: Set extended log in run time settings(F4)->Log->Extended Log->Data Returned by Server. Now I have recorded Facebook.com and used lr_debug_message. If the extended log is enabled it will print the message "I Love Facebook" else it will ignore the message. It will not print any message if the extended log is not enabled. lr_debug_message ( LR_MSG_CLASS_EXTENDED_LOG , "I Love Facebook" ); web_url ( "www.facebook.com" , " URL = http://www.facebook.com/ " , " Resource = 0 " , " RecContentType = text/html " , " Referer = " , " Snapshot = t1.inf " , " Mode = HTML " , LAST ); Example 2: With lr_set_debug_message In this example I have used lr_set_debug_message with lr_debug_message as s