The nuclei of trophozoites and digestive cysts as well as mitotic nuclei of several species of the vampyrellidsVampyrella, Gobiella, Hyalodiscus, Arachnula, andLeptophryswere investigated by electron microscopy. Except for some species of the genusHyalodiscus, the vampyrellids are generally multinucleate. The nuclei of the trophozoite stage are in interphase. These nuclei are spherical, except for the genusArachnula, which reveals elongated nuclei. In digestive cysts of all vampyrellids the nuclei enlarge and the pars granulosa of the nucleoli becomes prominent. Karyokineses take place synchronously in older digestive cysts, which transform into reproductive cysts. The nuclei divide by closed intranuclear orthomitosis. In telophase the old nuclear envelope disintegrates and a new one is rearranged. Only in the genusLeptophrysthe nuclear envelope decomposes before telophase. Neither centrioles nor MTOC‐plaques have been found in any stage of mitosis. After karyokinesis the cell divides inside the cyst or when leaving the cys