In the bacteriological study of intra-articular fluid in 22 children with rheumatoid arthritis the L-forms were isolated in 11. Of these, 7 had not been treated with preparations of the penicillin series. The complete isolation of the focus of inflammation from the environment and the presence of the L-forms of bacteria in the children who had not been treated with preparations of the penicillin series gave us grounds for conclusions on the etiological and pathological significance of the L-forms of streptococci in rheumatoid arthritis.