Intestinal microflora was investigated by fecal bacteriological examination in 175 patients with verified rheumatoid arthritis (RA). Intestinal dysbacteriosis of different stages was detected in 75 % of the RA patients on nonsteroid antiinflammatory treatment. The frequency and severity of abnormal biocenosis in RA patients were significantly greater than in subjects with osteoarthritis deformans (p<0.01) and bronchial asthma patients (p<0.01). Dysbacteriosis severity increased with growing RA activity (between the groups with the activity stage I and III the difference was significant, p<0.05). After the fecal microorganisms inoculation it became evident that RA patients carry, as a rule, Clostridium perfringens. Seven RA patients diagnosed to have dysbacteriosis received adjuvant bactisubtil (dry culture of the strain Bacillus IP 5832). The addition of bactisubtil aggravated the patients' condition, in 4 patients, moreover, the microflora got worse. Explanations of the observations on the direct participation of the intestine in RA pathogenesis are suggested.