This study is designed as a contribution to research into special-language use in oral contexts. Dialogue analysis is applied to the instruction given to apprentices during their training as prospective automobile mechanics. The focus is on the way in which the master mechanic conveys the necessary specialized knowledge to his charges. Alongside the organization of the subject matter the study examines the linguistic procedures involved in explaining specific professional techniques and processes, conveying the meaning of specialized vocabulary and testing the knowledge of the trainees. The final section looks into dialogue behaviour with a detrimental effect on the communication of specialized knowledge. The volume also contains a complete transcript of the corpus drawn upon.