The growth of fission yeast cultures was reversibly inhibited by exposure to the myosin-ATPase inhibitor 2,3-butanedione-2-monoxime (BDM). Wild-type cells treated with 20 mM BDM for approximately two generation times were smaller than untreated controls and had a septation index approximately twice that seen in the absence of the inhibitor. The organization of actin at the cell poles was somewhat disorganized in the presence of BDM; however, cells formed a cytokinetic actin ring. When nitrogen-starved stationary-phase cells were reinoculated into fresh medium in the presence of BDM, the time taken to repolarize the actin cytoskeleton and to resume the characteristic vegetative cell shape before initiation of the first cell division were both substantially delayed. BDM significantly inhibited the increase in cell length of cdc25.22 cells arrested for cell cycle progress by incubation at the restrictive temperature and substantially delayed the initiation of both mitosis and cytokinesis in arrested cdc25.22 cells after release of the temperature block. These results suggest that tip growth and cytokinesis--processes in fission yeast that involve the actin cytoskeleton--also require myosin activity.