The diagnosis of submucosal tumors, extrinsic lesions of gastrointestinal tract and mediastinal or celiac masses can be made by endoscopic ultrasonography (EUS) but histological confirmation (benign or malignant lesion) is still required. The aim of this study was to determine the efficacy of a new method, enabling EUS (curved array transducer)--guided fine needle aspiration of deep lesions. From October 1991 to August 1992, EUS-guided fine needle aspiration was performed in 26 patients in whom a mediastinal mass (6 cases), mediastinal lymph nodes (4 cases), submucosal tumor (5 cases), extrinsic masses (4 cases) and large fold gastric disease with negative endoscopic biopsy (7 cases) was detected by EUS. Diagnostic results were obtained in 19 of 26 patients (73.1%). A malignant tumor was detected in 21 of 26 patients. The EUS-guided fine needle aspiration was positive in 16 cases. The sensitivity for diagnosis of malignancy was 76.2% while specificity was 100%. The development of this new technique in the future needs further study.