Rheumatoid factors were found in 12 of a total of 105 SLE patients. 2. Rheumatoid factors were found especially in patients with additional chronic polyarthritis, whereas it was not possible to find a relation between these factors and the age of patients and the duration of disease, respectively. 3. There was no difference between SLE and progressive polyarthritis as regrads the cold precipitation of rheumatoid factors. 4. In vitro fixation of the complement to antinuclear factors was not hindered by rheumatoid factors. 5. Renal lesions and uremia were observed in SLE patients with and without rheumatoid factors, the percentages being roughly the same in the two groups.