The aim of the present study was to determine the significance of the lymphocyte transformation test with phyto-hemagglutinin in connection with the degree of inflammatory activity and serological changes. Lymphocyte transformation test with phytohemagglutinin was performed on 46 of the patients with rheumatoid arthritis active stage, diagnosed according to the New York criteria. In patients with low and moderate inflammatory activity the lymphocyte transformation test has values close to those of the controls. In patients with high inflammatory activity either low values or considerably higher were established as compared with the control group. The values of the test were proved, through the statistical analysis, to be heterogenous quantities in seropositive and seronegative patients.