Supraphysiological temperatures are generated by radiofrequency and microwave probes used for the treatment of prostate cancer (Montrosi et al., 1992) and benign prostatic hyperplasia (Larson et al., 1996). A quantitative understanding of the cellular mechanisms of tissue destruction due to these supraphysiological temperatures(> 40°C) is necessary for optimal application of clinical therapeutic protocols on the prostate and other tissue systems. A multitude of biophysical and biochemical events take place at the cellular level due to thermal stress (Cravalho et al., 1992). Some of the events include hyperpermeability of the membrane, denaturation of proteins, changes in cytoskeleton, alteration of intracellular ionic concentration and nuclear degradation. This study quantifies membrane injury by measuring the dynamics of vital dye leakage (Calcein) and Propidium Iodide (PI) uptake in the AT-1 Dunning rat prostate tumor cell line. Membrane injury (using these two dyes) is compared to the clonogenicity of these cells after comparable thermal insult. An Arrhenius damage model has been constructed for each of these assays based on a damage parameter to obtain the activation Energy (E) and frequency factor (A), which may prove useful in obtaining insight into the mechanisms of damage associated with thermal injury.