Brains from patients with Alzheimer’s disease are characterized by extracellular depositions of β-amyloid peptide (Aβ) and an intracellular accumulation of paired helical filaments (PHF) consisting of hyperphosphorylated tau proteins. The normal phosphorylation of tau protein controls microtubule polymerisation and stabilization, whereas its abnormal phosphorylation probably favours its dissociation from microtubules, its self-aggregation into PHF and its location in the somato-dendritic compartment. Aβ peptides have been shown to induce cell death in vitro and in vivo (Loo et al., 1993; Li et al., 1996.; Chen et al., 1996), but the connection between Aβ and tau phosphorylation is not clear. To shed light on this issue, tau phosphorylation was studied in rat PC 12 pheochro-mocytoma cells and Chinese hamster ovary (CHO) cells transfected with human tau-cDNA. Here we report a different phosphorylation pattern of tau in PC 12 and transfected CHO cells. Moreover, we examined the expression pattern in the two cell lines of glycogen synthase kinase-3β (GSK-3β) and the mitogen activated protein kinase (MAPK), both of which have been implicated in tau phosphorylation (Ishiguro et al., 1993; Mandelkow et al., 1992; Drewes et al., 1992).