Fifty-six patients with rheumatoid arthritis (RA) were assessed on two occasions three months apart. They completed two health status instruments--the Arthritis Impact Measurement Scales (AIMS) and the Nottingham Health Profile (NHP)--and the Beck Depression Inventory. In addition, clinical and serological data were gathered in order to calculate severity of disease according to the Mallya and Mace index. Health status instruments and the severity of disease index showed agreement in the assessment of mobility; similar agreement was found for different assessments of emotions. However, the two instruments provided social interaction scores with little agreement either cross-sectionally or in terms of change over time. It is argued that the generic NHP may be a valid instrument as an outcome measure in RA but the NHP and AIMS assess different aspects of social interaction. Care is needed in the selection of outcome measures to evaluate interventions.