Several studies have suggested that thermal therapy has a beneficial effect on degenerated intervertebral discs. Possible therapeutic mechanisms include collagen denaturation, cell ablation, and nerve tissue coagulation, however the precise mechanism or combination of mechanisms is unknown. To investigate the in vivo effects of thermal therapy on intervertebral discs using a murine model, a monopolar RF heating probe was developed and characterized. In addition, the effect size of several different thermal exposures was investigated by quantifying regions of cell death and collagen denaturation in rat discs. The heating probes were fabricated to have a 0.3mm outer diameter, 0.9mm exposed heating tip, and contain a thermocouple to monitor probe temperature. Using less than 2 Watts of RF energy produced high temperatures close to the probe and a steep radial temperature falloff. Five discs were treated at each of seven thermal exposures: 80°C for 10min, 80°C for 1min, 75°C for 5min, 62°C for 10min, 55°C for 15min, 48°C for 15min, and 48°C for 5min. A cell death region was observed in all treated discs and was significantly greater at the 80°C for 10min exposure than any of the lower exposures. Denaturation area was significantly greater at the 80°C for 10min exposure than at the four lowest temperature exposures. Denaturation was not observed in the 48°C exposures and was inconsistent in the 55°C and 62°C exposures. These results demonstrate that it is possible to limit and target the effects of thermal therapy to a portion of the murine disc using this RF probe.