Acid-catalysed dehydration of the polyhydroxyalkyl chain of 6,6-dimethyl-2-( d- gluco-pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one and of 6,6-dimethyl-2-( d- manno-pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one gave 2-α- d-arabinofuranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one ( 3). In a similar way, 2-β- d-lyxopyranosyl-6,6-dimethyl-4,5,6,7-tetrahydroindol-4-one ( 8) and 2-β- d-lyxopyranosyl-4,5,6,7-tetrahydroindol-4-one ( 9) were obtained by dehydration of 6,6-dimethyl-2-( d- galacto-pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one and 2-( d- galacto-pentitol-l-yl)-4,5,6,7-tetrahydroindol-4-one, respectively. The structures of the new C-nucleosides described ( 3, 8, and 9) were elucidated by chemical and physical methods.