Ultrasonic examination is an established method used to differentiate between solid and liquid structures in the pleural space. It can estimate the volume of a pleural effusion and demonstrate whether the effusion is associated with loculations or adhesions. It is complementary to thoracoscopy. In the diagnosis of pleural disease ultrasonic-assisted thoracoscopy should only be used when the less invasive methods of diagnosis such as pleural aspiration for cytological, bacteriological and chemical examinations and needle biopsy of the pleura have not yielded a diagnosis. Although thoracoscopy is a relatively invasive procedure, it has the advantages of speed and accuracy in the diagnosis of pleural disease. This procedure is not widely used as it requires specialized instruments and equipment and may be time-consuming. The latter disadvantage may be minimized by the use of prior pleural sonography. The ultrasonic examination will indicate the optimal point of entry of the thoracoscopy to avoid adhesions. In order to evaluate feasibility, complications and clinical results in ultrasonic-assisted thoracoscopy, we investigated 687 patients with pleural diseases from 1987 to 1990. As prior induction of a pneumothorax under X-ray control was not necessary, the 20-30 min required for this procedure was saved in all patients. Very few complications were attributable to ultrasonic-assisted thoracoscopy as it could normally be performed under local anesthesia. A macroscopic diagnosis was made in 80% of malignant diseases and 77% of inflammatory diseases in our total of 687 thoracoscopies. The diagnosis of a malignant pleural effusion was confirmed histologically and cytologically in 95% of those 190 patients in whom it was present.(ABSTRACT TRUNCATED AT 250 WORDS)