Sodium β-glycerophosphate, a substrate for endogenous phosphatases, was utilized to investigate the requirement for protein phosphatases (PPs) in cell cycle progression of partially synchronized onion root tip cells. Treatment of cells at early mitotic stages resulted in subsequent accumulation of mitotic cells mainly at pro-metaphase to metaphase stage. However, some abnormal anaphase cells could also be noticed. Indirect immunofluorescence and electron microscopic studies revealed that this was due to disruption of interaction between microtubules and kinetochores. Biochemical analysis of the extracts of these arrested mitotic cells showed higher level of cyclin B. These results suggest the changes occuring are due to inhibition of β-glycerophospate sensitive protein phosphatases associated with microtubules and cyclin destruction pathway.