Subjective pain score, clinical assessment, 99m technetium joint uptake, infrared thermography, and thermistor skin temperature measurements were evaluated and compared in patients with rheumatoid knee treated with intra-articular hydrocortisone. In 11 patients with definite and classical rheumatoid arthritis, 10 of whom had unilateral knee involvement, the affected knee joints were assessed by the above techniques before and at intervals after treatment of up to 14 days. The anti-inflammatory property of the steroid therapy was shown by all the assessment parameters, values having decreased significantly from the pretreatment values. However, the only parameter still showing a statistically significant decrease on the 14th post-treatment day was 99mTc joint uptake. Correlations were obtained between the two clinical measurements assessed by a physician i.e. pain score and index of joint inflammation. Both of these also correlated with the 99mTc joint uptake but not with skin temperature measurements. Using the clinical assessments as a yardstick, 99mTc joint uptake seemed to provide a useful index of changes in disease activity in the group as a whole. However, skin temperature measurements by infrared thermography and by the thermistor were of considerably less value.