This paper investigates the discourse structure of the practical demonstration, particularly the effect produced by the presence of a visual display. The Practical Demonstration (PD), as used in technical education, differs from the lecture in having a visual display; the speaker carries out an operation as he explains it. This affects the structure of the discourse in the following respects: (1) there is a feedback mechanism whereby students can ask and be asked questions; (2) the visual display gives coherence to the verbal text at all levels of discourse; (3) paralanguage (indicating, gaze direction etc.) links the verbal text and the visual display and is therefore a major cohesive device; and (4) the visual display provides an ongoing source of reference for the text. The pedagogical implications of this are that students of Technical English must be sensitized to the way the speaker uses the visual display if they are to cope adequately with technical instruction in English speaking institutions. Samples of illustrative materials are included. (Author/AMH)