This demonstration presents the utility of USI prototyping (of computer-based systems) as a human factors engineering design tool. We will present our USI prototyping tool, its composition, and a sample application. Throughout the demonstration we will illustrate how prototype USIs can be generated quickly and efficiently for user evaluation and immediate insertion into system design. Our tool for prototyping USIs is called a “USI Prototyping System (USIPS).” USIPS is divided into four components: Imagetool, Fonttool, Dynatool, and On-Line Help. Imagetool is used to build static images of text and graphics. Fonttool is used to design the fonts used in the images. Dynatool is used to link these static images into user and event driven USIs that interface to real and or simulated data bases. As a result these USIs appear to work as they would in the target system. On-Line Help is used to provide unfamiliar users with information on how to operate USIPS. We will describe each of these components in the demonstration. USI prototyping is used to formally and informally study design options for the USI before coding takes place. As the system design is being developed, different ways of interacting with users and displaying information is studied at relatively little cost. These studies yield an effective USI design which can then be implemented. A large bonus of USI prototyping is that it enables early and congenial interaction with future users of the system. User working groups can be formed and included early in the USI design process. Since the user is actively involved in the USI design process, user acceptance problems would be kept to a minimum. USI prototyping is also used to provide rapid answers to questions arising during the system development process.