1 This paper assesses the variability in the response of patients with rheumatoid disease to a group of non-steroidal anti-inflammatory drugs (NSAID). 2 Thirty six patients were divided into three groups and each group received a set of four NSAID. The different drugs were each given three times daily for a week and the treatment order was randomised. 3 The study demonstrated marked variability and unpredictability in patient responses and cast doubt on the value of comparative trials of different NSAID.