This discussion of the educational potential of audiotape and videotape cassettes in distance teaching considers each medium individually, with examples of how the Open University has tried to exploit them in its teaching, and comments on some major differences between the two media and their implication for education. Characteristics of audiocassettes are addressed first, including their ability to convey certain kinds of abstract information quickly, their informality and flexibility, and the relative ease of their design and production for academic staff. Potential educational applications noted include their use for direct teaching, as support material (either to other components or to students themselves), as an audio resource, and for delivering straight talks. In considering video, the content and structure of one Open University video program is described. Aimed at teachers, this program used real-life school scenes of children learning mathematics. Other educational uses of video are considered, and it is concluded that video can work as a catalyst for group discussion, and that videos that are designed to use the "stop-start" capabilities of the technology will be effective for individual use by students. An analysis of the differences between audio and vidocassettes indicates that audiocassettes are currently more valuable as an educational tool. (LMM)