We have employed the Hypertext Transfer Protocol (HTTP) and Hypertext Markup Language (HTML) to develop an automated patient registration and random allocation system for use in a multi-institutional clinical trial. We made it available on-line to World Wide Web clients in each hospital through a user friendly graphical user interface. During experimental operation, the physicians found it satisfactory from the viewpoint of both ease of operation and response time. For the development of a graphical user interface in network-based information system for use in multi-institutional clinical trials, HTTP/HTML has several advantages over an ordinary client-server model. Therefore, we concluded that we would adopt HTP/HTML for the construction of user interfaces for physicians in each spital and for data managers in our coordinating center.