Tumour necrosis factor (TNF) antagonists or blocking agents represent a major advance in the treatment of rheumatoid arthritis (RA), but their use raises economic concerns because of the high drug cost. Population-based patient registers with clinical data allow the estimation of the proportion of patients with RA who are eligible for TNF antagonist therapy according to recent consensus statements on TNF-targeted therapy. Data were derived from a representative county-based (500,000 population) register of patients with RA. Of 894 patients aged between 18 and 70 years, 636 (71%) [females 80%, mean (SD) age 53.6 (12.2) years and mean (SD) disease duration 12.2 (9.3) years] had a clinical and radiographic examination. The eligibility for TNF-targeted therapy was estimated from the following criteria: (i) previous or current therapy with at least one disease-modifying antirheumatic agent (DMARD); and (ii) active disease. Disease activity criteria were set to 28-swollen joint count (28-SJC) > or = 6, 28-tender joint count > or = 6, and erythrocyte sedimentation rate (ESR) > or = 28 mm/hour or C-reactive protein (CRP) > or = 20 mg/L. Sensitivity analyses were performed varying some of these disease activity parameters. Of the 636 patients, as many as 526 (83%) had previously or were currently using DMARDs and 98 (15%) fulfilled both the DMARD and activity criteria, thus being the maximum number of patients considered for TNF-targeted therapy. If the most stringent criteria were used (ever DMARD, 28-SJC > or = 12 and ESR > or = 50 mm/hour or CRP > or = 40 mg/L) only 15 of the 626 (2%) would be candidates for TNF-targeted therapy. In a population of 1 million, assuming a prevalence of 2000 patients with RA under the age of 70 years, the number of candidates for TNF-targeted therapy would be 40 to 300, depending on the disease activity criteria. Stringent ESR and CRP criteria would lead to a major reduction in the number of eligible patients. These utilisation data imply annual drug costs in the range of $US 480,000 to $US 3,600,000 for TNF antagonists for RA per 1 million population. Further economic evaluations are needed to determine for which groups such treatment is warranted from a health economics perspective.