Computer assisted teaching in thoracic medicine (E.A.O.) is described for the recognition and diagnosis of pulmonary opacities. Two programmes were used, both designed specially for medical study:--the first programme was for the recognition of shapes for the beginner to read abnormal radiographs (chest opacities), and--a programme to teach the beginner the diagnosis and to formulate a diagnostic strategy (diagnosis of pulmonary opacities). Working areas consisting of an alpha-numeric keyboard with a display screen and a slide projector are at present installed in two CHU hospitals in Paris and are connected by a special telephone line to the central computer C1T12 (in the Faculty of Medicine). Four practicals, lasting about 6 hours and 22 simulated cases lasting 8 hours are provided each with illustrated commentaries for the different stages, covering the overall educational objectives of the medical practitioner. After two years of experimentation the method was given a good reception by the medical students. Full confirmation of the technique as well as an evaluation to compare the method to other forms of teaching are at present under study.