Designing Web-applications is considerably different for mobile computers (handhelds, Personal Digital Assistants) than for desktop computers. The screen size and system resources are more limited and end-users interact differently. Consequently, detecting handheld-browsers on the server side and delivering pages optimized for a small client form factor is inevitable. The authors discuss their experiences during the design and development of an application for medical research, which was designed for both mobile and personal desktop computers. The investigations presented in this paper highlight some ways in which Web content can be adapted to make it more accessible to mobile computing users. As a result, the authors summarize their experiences in design guidelines and provide an overview of those factors which have to be taken into consideration when designing software for mobile computers. ''The old computing is about what computers can do, the new computing is about what people can do'' (Leonardo's laptop: human needs and the new computing technologies, MIT Press, 2002).