Visual-analogue scales can be used to measure the subjective aspect of functional ability but, in a group of patients with severe rheumatoid arthritis, the severity of impairment of two predetermined functional tests was low in comparison with the severity of pain. Measurements of the ability to carry out these two functions, using visual-analogue and descriptive scales, and also using the time taken to perform the tasks, were not useful measures of the effectiveness of treatment of rheumatoid arthritis. Poor correlations were obtained between different measures of the same function and between different functions measured in the same way.