In a prospective study of 6 patients with classic rheumatoid arthritis, we evaluated 3 measures of disease activity: comprehensive joint swelling and joint tenderness counts, and ultrasonography of joints. After baseline data were obtained on these 6 patients, therapy with fenbufen, a new nonsteroidal antiinflammatory drug, was begun. Followup examinations were performed at 4 weeks and 24 weeks after baseline. There were statistically significant differences between joint tenderness and joint swelling findings and between joint tenderness and joint ultrasonography findings (P less than 0.05 by kappa test statistic). In comparisons of joint swelling and ultrasonography, no difference was found (P greater than 0.05). When measures of changes over 6 months were compared, there was a high concordance between improvement in joint swelling and improvement in joint ultrasonography (P less than 0.01). Our results demonstrate that clinical assessment of joint swelling provides an accurate measure of synovial effusion, as confirmed by the more objective ultrasound measurements.