From three patients suffering from gastro-enteritis, non-mannite-fermenting, dysentery-like organisms were isolated which showed marked serological relationship to X, Y and P119 strains of B. dysenteriae Flexner.

In carbohydrate peptone-water media the organism fermented glucose without production of gas. In Lemco broth, however, both acid and gas were produced from glucose. The only other carbohydrate which was fermented was saccharose, but fermentation was weak and occurred only when incubation was prolonged for several days.

The organism possesses the group antigen common to the whole Flexner group and also a new type specific antigen of its own. Therefore it must be regarded as a new, non-mannite-fermenting member of the Flexner group of dysentery organism.

This work was undertaken at the instigation of Prof. P. L. Sutherland, to whom I am indebted for assistance and advice in the preparation of this paper. My thanks are due to Mr S. J. Denyer, Chief Technician, who isolated the first strain and referred it for further examination. I also thank Mr Gordon Denton for technical assistance.

Subcultures of all three strains have been sent to the National Collection of Type Cultures in London. Samples of the specific antiserum may be obtained from this laboratory.