An algorithm (Stoke index) has been designed to give a global measure of disease activity in rheumatoid arthritis. This algorithm has been created as an easy to use flow diagram based on two objective laboratory measures (C-reactive protein and erythrocyte sedimentation rate), one subjective and two semi-objective clinical measures (morning stiffness, synovitis score and Ritchie articular index). Results of six clinical markers and seven laboratory markers of disease activity on a cohort of 371 rheumatoid patients have been used to evaluate the algorithm and compare it with a previously described index of disease activity (Mallya-Mace index). Principal component analysis validates its ability to measure disease activity. Sensitivity is described by the distribution of patients between the two index scores. Change in index score by patients over a 6-month period indicates reversibility. The Stoke index demonstrates greater sensitivity and reversibility than the Mallya-Mace index. These findings indicate that the algorithm described provides a useful index of global disease activity for use in the assessment of rheumatoid arthritis.