The increased use of audit and resource management within the health service will focus attention on variations in clinical practice. We have looked at one rheumatological example; the extent rheumatologists vary in their clinical use of a slow-acting anti-inflammatory drug. We studied a single drug - sulphasalazine. In a prospective study sulphasalazine was given to 298 rheumatoid patients at 24 rheumatology centres in South East England. They were followed for 6 months. There were large differences between centres in: the types of patient started on therapy; the numbers of patients remaining on treatment; the responses after 6 months. The difference between some centres was more marked than the expected improvement in clinical and laboratory variables given by sulphasalazine. The use of a slow acting anti-rheumatic drug like sulphasalazine in rheumatoid arthritis is agreed by most rheumatologists in the UK and yet there are wide variations in its use. Our results question the validity of comparing clinical practice and associated costs between centres for even a simple clinical procedure.