Dielectric spectroscopy was used to measure the dielectric relaxation of bovine serum albumin, Protein A, and rabbit IgG in solution. Measurements were performed with an impedance analyzer and dielectric cell. Protein additions to bulk solution were measured by differential dielectric relaxation spectroscopy, presented as a method to measure the individual contributions of proteins to relaxation phenomena and reduce effects of electrode polarization. Relaxation characteristics of the proteins individually and as a complex were observed. Frequency shifts in the relaxation characteristics indicate binding. This illustrates the potential use of bulk solution dielectric relaxation as the principle of operation for a biosensor.