Previous clinical ultrasound investigations have been adversely affected by inadequate knowledge of the focusing characteristics of the transducer. Precise knowledge of the beam width profile has substantial impact on routine diagnostic procedures and is essential for proper display of the anechoic nature of small cysts, tissue textures, and particularly the distal shadow which characterizes gallstones. In vitro and in vivo tests using transducers with various beam focusing profiles clearly demonstrate that optimal imaging performance occurs within a very narrow range at a critical distance from the transducer face.