The last 20 years have seen the clarification of a number of questions about the sources, mechanisms, and diagnostic meaning of lung sounds. These include the specificity of fine and coarse crackles for different diseases; the normal distribution of lung sounds over the chest; and the likely location of the source of the normal lung sound within the airways. Nevertheless, no instrument or signal processing scheme has yet proved to be more effective for analyzing lung sounds than the stethoscope. Several fundamental questions remain mysterious. They are: The mechanisms that produce the normal lung sounds (which appear to be remarkably independent of gas density); the causes of the inhomogeneous distribution of normal lung sounds over the chest wall; the reason that lung sounds are faint or absent in emphysema; and through what pathway(s) airway-generated lung sounds reach the chest wall. These questions must be answered before computer-aided lung sound analysis can fulfill its promise to reveal more information about pulmonary physiology and pathology than is now possible by ear alone.