The objective of this paper is to propose a telemedicine transaction model and a set of terms to facilitate communication between telemedicine researchers, program directors, and others. The model is described in terms of the sites, personnel, and events involved. Examples of real-time, store-and-forward, and physical referral transactions are depicted using the model. A hierarchy of information classes for collaboration studies is developed based on their relation to the frequency of data collection. Finally, a list of definitions is given to specify the terminology used. The model is suitable for most telemedicine systems, is useful in providing a common language for skilled telemedicine participants, and can be used in comparative evaluation studies.