A prototype fiberoptic gastroscope with a 9 MHz transducer 7 cm from its tip was used to evaluate intrinsic and extrinsic abnormalities of the upper abdomen and mediastinum. Small hepatic and pancreatic tumors were identified, often with more clarity than when other imaging modalities were used. The instrument clearly defined intrinsic bowel wall lesions including focal and diffuse disease. Bowel wall thickness was identified, and exact wall dimensions were measured. In addition, unsuspected pericardial, mitral, and aortic valvular disease was detected. These preliminary results suggest a new complementary imaging modality.