A strain of Spirochœta refringens has been obtained in pure culture, and its morphological and cultural characteristics have been studied. The strain possessed no pathogenicity for rabbits or monkeys. It probably belongs to the genus Treponema, but it is easily differentiated from Treponema pallidum, Treponema microdentium, and Treponema macrodentium. Its relation to Spirochœta balanitidis and Spirochœta buccalis is still undetermined.