A programme for rheumatoid factor (RF) measurement was sponsored by the South East Asian Pacific League against Rheumatism (SEAPAL) and the Clinical Immunology Group (CIG) of the Australian Society for Immunology. Measurements in 29 laboratories in 12 countries showed: a large variety of methods were being used to measure RF, most using semiquantitative agglutination techniques; some laboratories have invalid techniques; the quoted upper normal limit varied considerably between assays, and false positives were identified in three laboratories; a wide range of intralaboratory precision within and between assays; and a reduction in discordance between laboratories by the inclusion of local standards. Before international standardisation of RF measurement can be achieved attention to many of these problems is required. In particular we recommend the wider use of reference standards and the regular participation in quality control programmes in order to monitor performance.