Studies of the ultrasonic absorption of dipeptides, polypeptides, and hemoglobin are proposed in order to elucidate the nature of the interaction between ultrasound and proteins. A small volume, fixed path, variable frequency ultrasonic interferrometer capable of operating automatically over a three decade frequency range (100 kHz to 100 MHz) is proposed as the primary means of collecting the ultrasonic data. The systems to be investigated are chosen to exhibit three of the commonly proposed mechanisms by which ultrasound interacts with proteins; changes in the overall state of ionization of the protein; changes in the internal distribution of charge in the protein; and changes in the conformational state of the protein. It is expected that information concerning the rate of proton transfers between neighboring groups and kinetic parameters for the -helix to random coil transition as a function of molecular weight will be obtained. It is also proposed that evidence concerning the oxy-deoxy conformational change in hemoglobin will be found by studying the dependence of the ultrasonic absorption on oxygen content. The results of these experiments should contribute to both an understanding of the dynamical processes in proteins and to confidence in the efficacy and safety of ultrasound as a clinical tool.