The regulation of stathmin phosphorylation is complex and, in all likelihood, multifactorial. For example, phosphorylations at all four Ser residues fluctuate during the cell cycle and CDK2 has been identified as the kinase system involved in cell cycle-regulated phosphorylation of Ser38. Besides, three distinct protein kinases have been identified to phosphorylate stathmin in response to external signals. These kinases are members of the MAPK family that phosphorylates Ser25, cyclic AMP-dependent protein kinase (PKA) that phosphorylates Ser63 and CamKII that phosphorylates Ser16 [26] . Because the kinases acting at these residues are distinct and may be functioning through different pathways, it is reasonable to speculate that regulation of stathmin phosphorylation can be achieved by multiple pathways, thus providing the cell with a finely tunable mechanism for controlling microtubule assembly and dynamics in relation to its needs.