Examinations of 230 patients with local pyogenic infection and those of 117 patients with sepsis revealed that asporogenic anaerobes on pure culture were isolated in 17.8% with local pyosis and in 10.2% of patients with sepsis. Anaerobes along with aerobic microbes were found 15.6% of patients with local infection and in 10.2% of patients with sepsis. The involvement of obligate anaerobes in the development of pyogenic infection was displayed by the lower phagocytic activity of neutrophils, the impaired differentiation of lymphocytes, the great increased peripheral blood levels of O-cells, and diminished serum complementary, lysozyme, and overall bactericidal activities and IgM levels.