Eight strains of a previously undescribed coryneform bacterium had been isolated from human clinical material over a 5-year period. Colonies of the unknown coryneform bacterium had an unusual appearance as they were slightly yellowish and very mucoid. Biochemical and chemotaxonomic characterization revealed that the unknown coryneform bacterium belonged to the genus Corynebacterium. It could be readily differentiated from all previously described Corynebacterium species. Electron microscopy demonstrated the production of an extracellular substance causing connecting filaments between cells as a morphological correlate to the mucoid colonies. Comparative 16S rRNA gene sequence analysis revealed that the unknown coryneform bacterium represented a new subline within the genus Corynebacterium, for which the name Corynebacterium mucifaciens sp. nov. is proposed. The type strain is CCUG 36878 (= DSM 44265 = CIP 105129).