IN PAST AUDITING OF COMPUTERIZED SYTEMS, THE AUDITOR'S OBJECTIVE WAS TO DETERMINE WHETHER THE SYSTEM WAS OPERATING IN ACCORDANCE WITH DESIGN SPECIFICATIONS AND APPLICABLE POLICIES AND PROCEDURES. THE METHODS USED ENABLED THE AUDITOR TO EVALUATE SPECIFIC ASPECTS OF COMPUTERIZED SYSTEMS (INPUT CONTROLS, PROGRAMMING CONTROLS, OUTPUT CONTROLS, OR SYSTEM PERFORMANCE), BUT SELDOM WAS THE ENTIRE SYSTEM REVIEWED AT ONE TIME, UNLESS THE AUDITOR INTEGRATED A TEST FACILITY INTO THE SYSTEM'S DESIGN. THE METHODOLOGY PROPOSED (THE SIMULTANEOUS-PARALLEL APPROACH TO AN INTEGRATED TEST FACILITY) PROVIDES FOR TESTING THE INTERNAL CONTROLS AND PERFORMANCE OF AN ENTIRE COMPUTERIZED SYSTEM, EVEN THOUGH THAT SYSTEM HAS BEEN OPERATIONAL FOR YEARS. TEST TRANSACTIONS ARE ENTERED INTO THE SYSTEM AT THE SAME TIME AS LIVE TRANSACTIONS, AND, ONCE IN THE SYSTEM, TEST TRANSACTIONS ARE PROCESSED SEPARATELY UNTIL THE FINAL OUTPUT PHASE, WHERE THEY ARE MERGED WITH LIVE DATA FOR ON-LINE TRANSMISSION BACK TO THE INITIATOR. THE APPROACH REQUIRES LITTLE PROGRAM MODIFICATION, RELYING MAINLY ON THE JOB CONTROL LANGUAGE OF THE OPERATING SYSTEM AND TWO NEW PROGRAMS--SPLITTING TEST FROM LIVE TRANSACTIONS AND MERGING THEM BACK TOGETHER. THE ONLY MAJOR DRAWBACK OF THE SYSTEM IS THE ALLOCATION OF THE DIRECT-ACCESS DEVICES FOR STORING TEST RECORDS. IT MAY NOT ALWAYS BE FEASIBLE TO ACQUIRE THESE DEVICES; IF THE SYSTEM BEING TESTED IS SMALL ENOUGH AND NOT TIME DEPENDENT, TEST RECORDS CAN BE ALLOCATED TO MAGNETIC TAPES. THE METHODOLOGY IS DETAILED USING GRAPHIC ILLUSTRATIONS. (RCB)