AbstractPrevious work on five cell types isolated from the bovine corpus luteum showed that the mass of acetylated microtubules (acet‐MTs) in interphase differed. Endothelial cells, termed type 3, showed few acet‐MTs, whereas the interphase cytoskeleton of granulosal‐like cells, termed type 5, was rich in acet‐MTs. In the present study, these cultured cells were used to determine whether the degree of α‐tubulin acetylation in interphase had consequences on mitosis. To this end, the distribution of acet‐MTs was determined throughout the cell cycle using a monoclonal antibody, 6‐11B‐1, directed against acetylated α‐tubulin. For comparison, tyrosinated MTs were visualized with another monoclonal antibody, YL1/2, detecting tyrosinated α‐tubulin. Although the amount of acet‐MTs in interphase differed significantly between both cell types, major differences in the appearance of acet‐MTs during mitosis were only apparent in prophase and during transition from late telophase to interphase. Thus, irrespective of different α‐tubulin acetylation in interphase, spindle structure is uniform. Since acetylation of α‐tubulin is believed to indicate the presence of relatively stable MTs, we conclude that MT dynamics is differently controlled in interphase and mitosis. Thereby interphase cells are able to carry out functions which involve stable MTs and the cells progress through mitosis in