A simple method of assessing 'index of disease activity' (IDA) in rheumatoid arthritis (RA) using a multivariate analysis (MVA) comprising morning stiffness (MS), pain scale (PS), grip strength (GS), articular index (AI), haemoglobin (Hb) and erythrocyte sedimentation rate (ESR) is described. The IDA of 99 patients with RA was assessed using MVA. The method could be used reliably and readily for random or longitudinal assessment, in drug trials and for comparing disease activity with other objective indices.