A new experimental design was developed to study the value of clinical parameters of disease activity in patients with rheumatoid arthritis. Ten patients with classical rheumatoid arthritis were examined by five senior doctors in a department of medical rheumatology. In spite of an attempt to make the clinical examination as uniform as possible the inter-observer variation among the doctors was greater than the variation among the patients, for the following parameters: joint pain at rest, joint tenderness and joint swelling. An acceptable inter-observer variation in relation to patient variation was found for 1) a combined registration of joint pain at rest or on movement, 2) duration of morning stiffness, 3) grip strength, 4) subjective well-being as indicated on a visual analogue scale, 5) fingertip--palm distance, and 6) maximum flexion-extension in elbows, wrists and knees. The variation from morning to afternoon and from day to day was negligible. It is concluded that registration of elaborated articular scores is useless in the daily routine in rheumatological departments when different doctors examine the patients.