The prognostic value of quantitative measurement of rheumatoid factor (RF) by immunoturbidimetry was evaluated in 78 patients with early rheumatoid arthritis (RA) during a 3-yr follow-up. After starting disease-modifying antirheumatic treatment, a significant improvement in conventional clinical and laboratory variables measuring disease activity was observed, while a steady increase was found in radiological progression. Initial RF levels correlated with radiologically determined joint damage up to 3 yr, whereas no correlation of other initially determined conventional variables of disease activity was found. High levels of RF at entry and persistent RF positivity during the follow-up were markers for destructive disease. Initial RF positivity alone was a sensitive predictor for later joint destruction, but quantitative measurement of the initial RF level and especially repeated measurements of RF seemed to add significantly to the prognostic value of RF in distinguishing between progressive and non-progressive disease in early RA.