Tissue electrical impedance is a function of its architecture and has been used to differentiate normal and cancer tissues in a variety of organs including breast, cervix, skin, and bladder. This paper investigates the possibility of differentiating normal and malignant prostate tissue using bioimpedance spectra. A probe was designed to measure impedance spectra over the range of 10 kHz to 1 MHz. The probe was fully characterized using discrete loads and saline solutions of different concentrations. Impedance spectra of five ex vivo prostates were measured in the operating room immediately following radical prostatectomy. Wilcoxon signed-rank tests were used to compare the normal and malignant findings. The impedance probe had a signal-to-noise ratio (SNR) > 84 dB across the entire spectrum and measured a tissue volume of approximately 46 mm(3). At 10 kHz, prostate conductivity (or) ranged from 0.232 S/m to 0.310 S/m for tumor and from 0.238 S/m to 0.901 S/m for normal tissue. At 1 MHz the ranges were 0.301 S/m to 0.488 S/m for tumor and 0.337 S/m to 1.149 S/m for normal. Prostate permittivity (epsilonr) ranged from 6.64 x10(4) to 1.25 x 10(5) for tumor and from 9.08 x 10(4) to 4.49 x 10(5) for normal tissues at 10 kHz. And, at 1 MHz the er ranges were 9.23 x 10(2) to 1.88 x 10(3) for tumor and 1.16 x 10(3) to 2.18 x 10(3) for normal tissue. Both sigma and epsilonr of tumor tissue were found to be significantly lower than that of normal tissue (P < 0.0001). Conductivity and permittivity are both higher in normal prostate tissues than they are in malignant tissue making them suitable parameters for tissue differentiation. This is in agreement with trends observed in other tissues reported in much of the literature. Expanded studies are needed to further validate this finding and to explore the biological mechanism responsible for generating the results.