Objective: To evaluate and compare the effects of locally applied heat and cold treatments on skin and intraarticular temperature in patients with arthritis. Methods. Thirty-nine patients with arthritis of the knee were divided at random into 4 treatment groups (ice chips, nitrogen cold air, ligno-paraffin, and placebo short wave). A temperature probe was inserted into the knee joint cavity and another placed on the overlying skin, and changes in temperature over 3 hours were recorded for each treatment group. - Results: The mean temperature of the surface of the skin dropped from 32.2°C to 16.0°C after application of ice chips and from 32.6°C to 9.8°C after application of nitrogen cold air; the mean intraarticular temperature decreased from 35.5°C to 29.1°C and from 35.8°C to 32.5°C, respectively, after these treatments. Treatment with ligno-paraffin increased the surface temperature by 7.5°C and the temperature in the joint cavity by 1.7°C. No significant changes were observed with placebo short wave diathermy. - Conclusion: The traditional model, that intraarticular temperature is decreased by superficial heat and increased by superficial cold, must be discarded. In arthritis patients, intraarticular temperature is increased by superficial heat and decreased by superficial cold. This has clear consequences for treatment policy.