This is the fourth volume of Ultrasound in Medicine, the Proceedings of the Annual Scientific Meeting of the American Institute of Ultrasound in Medicine. Unless the Executive Board of the Institute change their mind, it may also be the last. Under these circumstances it is somewhat ironical that some of the deficiencies present in previous volumes appear to have been solved in the present volume. Notably, the Programme Committee, for the first time, exercised a stringent selection procedure by means of which the number of papers selected for presentation was limited with the result that both the quality of papers accepted for presentation and publication was improved and the number of simultaneous sessions at the meeting did not exceed two. The contents of this volume have been divided into the same sections as in previous volumes except that no papers on stan dardization procedures were accepted and a new supplementary section is added consisting of papers given at the Scientific Meeting of the American Society of Ultrasound Technical Specia lists. As in previous editions the readers may consider the engin eering sections at the end of this volume are the most rewarding. Some ingenious new systems are described both in the sections on Doppler techniques and new techniques. Current interest in tissue signatures and characterization are reflected in many of the pap~rs appearing in the Tissue Interactions section.