In a prospective study, A mode ultrasound scanning contributed to the diagnosis and management of 24 of 50 consecutive patients with pleural disease. In 30% of patients it was superior to radiology in clarifying the solid or fluid nature of a pleural opacity, and in 42% of patients it allowed selection of the most appropriate site for the aspiration of pleural fluid. The technique is simple and the apparatus is widely available. We believe that ultrasound is an important practical aid in the diagnosis and management of pleural disease.