Abstract Loaded under whole cell patch-clamp configuration, the caged Ca 2+ molecule DM-nitrophen was used to increase [Ca 2+] i rapidly and reversibly in isolated Deiters cells of the organ of Corti. Photolysis of DM-nitrophen increased [Ca 2+] i from resting concentrations of 20-50 nM to values above μM, as measured with the fluorescent indicator Fluo-3. Immediately after the photoliberation of Ca 2+ a movement of the head of the phalangeal process could be observed in 75% of cells (n=28). This mechanical movement, with an amplitude ranging between 0.5 to 1 μm within few hundred of ms, consisted of an extension of the phalanges away from the cell body. Measurement of phalangeal stiffness in transversal flexion toward the cell body ranged between 15-440 pN/μm. Stiffness can increase by 28 to 51% after rising [Ca 2+] i. The results suggest Ca 2+ as a potential intracellular messenger for active mechanical responses in Deiters cells.