Biopsies from typical lesions of pitted keratolysis from five patients have been investigated by electron microscopy to provide information on colonization and morphology of the microorganisms involved in this disease. A part of the biopsies was inoculated in culture media, and Corynebacteria were selected for further examination. Electron microscopy revealed a great variability in the morphologic feature of bacteria concerning size, shape, capsule, cell wall, cross wall formation, plasma membrane, nucleoplasm, cytoplasmic organelles and constituents including mesosomes, ribosomes, volutin granules, and glycogen particles. The pleomorphism is thought to be due in part to the diversity of preparation techniques used in this study and in part to different growth conditionsin vivoandin vitro.As a consequence the present findings are only partly comparable with previously published data on bacteria involved in skin diseases. Evidence is presented that bacteria inducing pitted keratolysis may be able to destroy keratin by means of hydrolytic enzymatic activity.