The authors describe a method of enzymo-immunological estimation of rheumatoid factor. This estimation, of non-competitive type, includes 3 stages : the rheumatoid factor is first extracted from the serum by fixation on the aggregated IgG linked to cellulose powder; then its presence is revealed by fixation of an oxidase IgG glucose conjugate on the solid phase; finally, the enzyme activity linked to the solid phase is measured. This activity is directly related to the concentration of rheumatoid factor present. The estimation, carried out on 2 050 patients including 114 with rheumatoid arthritis, is well correlated with technic of the Rose-Waaler reaction. Furthermore, the greater sensitivity, the better reproducibility and the quantitative character of this method might improve the supervision of patients with rheumatoid arthritis.