The nuclear division of a free-living bodonid flagellate was investigated at the ultrastructural level for the first time. Transmission electron microscopy of serial ultrathin sections shows that nuclear division of Bodo curvifilus occurs by closed mitosis with an intranuclear spindle, as in trypanosomatids and cryptobiids. The nucleolar material of B. curvifilus persists during the nuclear division and seems to be shared between the daughter nuclei. The spindle consists of one compact bundle of approximately 30 microtubules running through the nuclear centre: most of the microtubules continue from one pole to another. Microtubule-organising centres of the mitotic spindle lie at the opposite poles, and they are not distinguished morphologically. The spindle of B. curvifilus is associated with at least 10 pairs of kinetochore-like dense plaques. In sections only the plaques can be seen at different stages of migration towards the poles as chromosomes are not condensed during mitosis of kinetoplastids.