The voltage-gated calcium channel Cav1.3 carries >90 % of the Ca2+ current in inner (IHC) and outer (OHC) hair cells and is crucial for HC development and exocytosis. Voltage gated calcium channels consist of the pore forming alpha1 and the auxiliary subunits (SU) beta, gamma and alpha2delta. Beta subunits are encoded by four distinct genes and can modulate biophysical properties and trafficking of the channels. We attempt to identify the associated beta SUs to find reasons for the specific properties of Cav1.3 currents in hair cells. We performed RT-PCR using specifically isolated IHCs or OHCs and preferentially detected beta1 in IHCs and beta3 in OHCs, but occasionally also beta-2 and beta-4. Ba2+ currents (IBa) were measured in beta3-deficient mice (beta3-/-) and controls in IHCs (P2-P22) and OHCs (P1-P7). No difference in IBa amplitudes or the voltage-dependence of activation could be detected in beta3-/-versus beta3+/+ animals in both types of hair cells. In beta3-/-OHCs (P5) IBa was 20.5±6.0 pA, n=6, compared to IBa in beta3+/+ OHCs (P6) of 24.6±6.3 pA, n=7. In IHCs, IBa was 238 ±56 pA (n=4) and 240±109 pA (n=3) for beta3-/- and controls at P22, respectively. These results suggest that lack of the beta3 SU either does not influence IBa properties or can be compensated by another beta SU in inner and outer HCs. Supported by DFG En294/2-4 and FSP Baden-Wuerttemberg