Synchronous populations of CV-1 cells have been prepared by the selective detachment of mitotic cells. An approach, using a combination of standard techniques, has allowed evaluation of the degree of synchrony throughout the cell cycle. CV-1 cells have a cycle of approximately 19-hr duration, throughout which synchronous populations progress with a dispersion of 3 hr, i.e., ie, greater than or equal to 90% of the cells enter S phase and subsequently divide within a 3-hr period. A major cause of this dispersion is the differential attachment times of individual cell within the population when a synchronous culture is initiated.