The IgM, IgG and IgA rheumatoid factors (RF) were studied by ELISA in the serum of 122 patients with rheumatoid arthritis (RA) associating the Waaler-Rose test results, with the clinical and radiological aspects of the disease. 75 patients (61%) had RF IgM positive according to the Waaler-Rose test while the ELISA showed positive in 104 (85%). The RF (IgG was positive in 64 cases (52%) and RF IgA in 82 (67%). The levels of RF IgA were correlated to RF IgM levels, determined by the Waaler-Rose test (p < 0.01) and ELISA (p < 0.001), while RF IgG levels were not correlated to RF IgM or IgA. There was a significant correlation between RF IgA titles and Lansbury's index (p < 0.01), and between RF IgG and sedimentation rate (p < 0.01). In patients with extraarticular disease high levels of RF have been observed, especially RF IgM and IgA. We concluded that the ELISA technique is the preferred method to measure the RF.