Early diagnosis and treatment of rheumatoid arthritis (RA) is necessary to prevent joint damage and long-term disability. High rates of false-negative and false-positive results of the rheumatoid factor (RF) test make it generally unhelpful in the early diagnosis of RA. A new clinical test for RA--the anti-citrullinated peptide antibody (ACPA) test--is now widely available in Australia. Owing to its high specificity (95%), a positive ACPA test result usually confirms a diagnosis of RA in a patient with undifferentiated inflammatory arthritis. The superior specificity of the ACPA test provides an argument for it to replace the RF test in the primary care setting. Performing both tests adds little to the use of the ACPA test alone. An early diagnostic opinion from a rheumatologist is still recommended, as the ACPA and RF tests frequently return negative results in early RA.