A technique and an original apparatus for recording and displaying the sound levels emitted by human lungs during respiratory movements are described. A graphic recording of chest acoustics can be obtained. An analysis of the phonopneumographic findings showed clear differences between normal and pathological readings, both in the level of the sounds and in their frequency content. Evidence was given of cases in which the physician can directly recognize the presence of special diseases. Beside this, FPGraphic representations are also useful for retaining evidence of findings which cannot be recorded by other methods, and for checking the natural evolution of a disease or its response to clinical treatments.