This paper has presented a compilation of facts gained from the study of 290 cases of skin infections produced by Mycobacterium balnei. All of these infections apparently stemmed from a common source. We are unable to trace the introduction of the infectious organism into the particular swimming pool in question. We have related the clinical, bacteriological, and public health aspects of this epidemic as recorded by private physicians, a private bacteriologic laboratory of a philanthropic institution, and a state public health department.