Mitosis in spherical cells of heteronuclear cell line VUP-1 was analyzed by means of time-lapse cinemicrography. A comparison with another permanent cell line (hamster) revealed some differences in the duration of individual mitotic stages. Metaphase was the longest stage in VUP-1 line cells (about 3-4 hours). Various irregularities in mitotic cycle kinetics were also found, such as absence of anaphase or separation of chromosomes from the aster in metaphase. Attention was further focussed on cytokinesis.