In a prospective study of up to 3 years' duration of 113 patients with early rheumatoid arthritis a disease activity score (DAS) was developed based on the clinical judgment of 6 rheumatologists. The patients were divided in groups with high and low disease activity according to explicit rules. By various statistical methods, including discriminant analysis and multiple regression analysis, a DAS could be defined. This DAS is a continuous measure consisting of the variables Ritchie articular index, number of swollen joints, erythrocyte sedimentation rate and general health measured on a visual analog scale.