The focal adhesion kinase (FAK), a non-receptor tyrosine kinase, plays an important role in cell migration, cell proliferation and cell survival. Since these processes participate in the restoration of tubular integrity in renal ischaemia and reperfusion (I/R), FAK expression and phosphorylation at Tyr-397, the latter indicative of its activity, were examined in the different kidney zones by Western blot analysis and immunohistochemistry. Expression and phosphorylation of FAK were studied in MDCK and medullary thick ascending limb (mTAL) cells following ATP depletion and repletion. In control rat kidneys, FAK expression was higher in the outer and inner medulla than in the cortex and phosphorylation was most pronounced in the inner medulla. While the FAK expression pattern was not affected by 20 min ischaemia and 20 min ischaemia followed by 60 min or 24 h reperfusion, FAK phosphorylation was significantly reduced in all kidney zones immediately after ischaemia, but increased during reperfusion, exceeding even control values in the outer and inner medulla. ATP depletion and repletion of MDCK and mTAL cells was associated with a decreased FAK phosphorylation during ATP depletion, followed by an increase during repletion. The morphologic changes during depletion/repletion were visualized by immunofluorescence microscopy. During ATP depletion focal adhesions were disrupted. Their reformation after repletion paralleled the increase in FAK phosphorylation. These findings suggest an essential role for FAK-signalling during renal I/R.