The AppendToLog method adds a string to the end of the Web server log entry for this request. You can call it multiple times in one section of script. Each time the method is called it appends the specified string to the existing entry.
Response.AppendToLog string
In order for the specified string to be recorded in the log file, you must enable the URI Query option of the Extended Logging Properties sheet for the site whose activity you wish to log. For more information on configuring Extended Logging, see Customizing W3C Extended Logging.