Conventional application of radiofrequency (RF) energy for thermotherapeutic ablation of pathological tissue is limited by tissue desiccation, high electrical impedance, and small lesion size. A new method has been developed which allows controllable production of small to large lesions. This technique modifies the electric field within the tissue by interstitially infusing hypertonic saline during the application of RF energy. The present study was conducted to determine the spread of saline in prostate and resultant impedance changes. A 26 gauge needle with 5mm exposed metal tip was inserted into the prostate of 10 canines. Impedance measurements were made between the two recording electrodes placed 12mm apart, with the infusion electrode at the center. Hypertonic saline (14.6% NaCl) with a 35% mixture of a radiocontrast agent (Hypaque) was continuously infused at 2 ml/min through the needle electrode into the tissue for 10 minutes. Fluoroscopic images were taken concomitantly with impedance measurements. The images were analyzed for intensity and spread of the saline concentration field. The developed concentration field was observed to modify the impedance characteristics, thereby indicating the creation of the saline-liquid electrode. This research has facilitated the development of RF hyperthermic treatment for benign prostatic hyperplasia in humans.