Variably acid-fast coccoid forms, suggestive of acid-fast, cell-wall-deficient forms of mycobacteria, were observed in microscopy of sections of skin from three patients with mycosis fungoides. Similar coccoid forms were also seen in sections of the heart, lung, liver, lymph nodes, connective tissue, and other organs of one of them who died, and in biopsy material from lymph nodes obtained one year antemortem in that patient. The present findings of microbes in mycosis fungoides may be related to the previous findings of acid-fast bacteria in mycosis fungoides and other malignancies as reported by other investigators. The present histopathologic findings also suggest that mycosis fungoides may be an infectious disease of mycobacterial origin.