This paper reports on research to investigate design features of asynchronous discussion systems for higher education. The research aims to identify features that increase the benefits of discussion systems and reduce the problems. The paper focuses on a major theme that emerged from interviews with learners and teachers: information overload. Interview findings, together with literature and system reviews, were used to identify four areas of possible system enhancement aimed at alleviating overload: branched message threading; user recommendations of messages; message filtering; and a personal 'clippings' area for useful messages. The paper discusses these enhancements and their evaluation in a prototype discussion system used on a UK Open University course. Data from the student evaluation indicated that students preferred branched threading to linear threading; they thought filtering and clippings were helpful in principle, although they did not use them very much; and they felt uncomfortable with the idea of recommending each others' messages. Students felt less overloaded in the second part of the course, which was when the system enhancements were made available.