Pheochromocytomas and paragangliomas (PPGLs) with activated pseudohypoxic pathways are associated with an immature catecholamine phenotype and carry a higher risk for metastasis. For improved understanding of the underlying mechanisms we investigated the impact of hypoxia and pseudohypoxia on catecholamine biosynthesis in pheochromocytoma cells naturally lacking Hif2 alpha (MPC and MTT) or expressing both Hif1 alpha and Hif2 alpha (PC12). Cultivation under extrinsic hypoxia or in spheroid culture (intrinsic hypoxia) increased cellular dopamine and norepinephrine contents in all cell lines. To distinguish further between Hifla- and Hif2 alpha-driven effects we expressed Hif2 alpha in MTT and MPC-mCherry cells (naturally lacking Hif2 alpha). Presence of Hif2 alpha resulted in similarly increased cellular dopamine and norepinephrine under hypoxia as in the control cells. Furthermore, hypoxia resulted in enhanced phosphorylation of tyrosine hydroxylase (TH). A specific knockdown of Hif1 alpha in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2 alpha under normoxia resulted in increased TH phosphorylation, further stimulated by extrinsic hypoxia. Correlations with PPGL tissue data led us to conclude that catecholamine biosynthesis under hypoxia is mainly mediated through increased phosphorylation of TH, regulated as a short-term response (24-48 h) by HIf1 alpha. Continuous activation of hypoxia-related genes under pseudohypoxia leads to a HIF2 alpha-mediated phosphorylation of TH (permanent status).