A series of studies is described in which a hypermedia system was introduced into an undergraduate biology curriculum. The aim of these studies was to investigate the patterns of students' interaction with and attitudes to the system, both to develop the interface of the system itself, and to provide objective means of describing its use in a realistic learning situation. A novel set of performance descriptors was developed to enable the second of these objectives. These descriptors are based on quantitative data easily obtainable by automatically logging student interactions with the system, and are applicable to any data set and any system, not just those described here. Using these descriptors, a number of different factors - the task being performed, interface characteristics and individual differences - were demonstrated to have an effect on the students' patterns of interaction with the system. In addition, qualitative data are presented, demonstrating that the reaction to the system was extremely positive. The development of StackMaker, the hypermedia system used to create the biology materials, is also described. StackMaker was intended to encourage subject specialists to become involved directly in the authoring of hypermedia learning materials. A number of case studies of authors using Stackmaker are presented, and initial authoring strategies are discussed.