The lateral membrane of mammalian cochlear outer hair cells contains a membrane protein, prestin, which can act as a fast actuator driving electromotility and ultimately cochlear amplification. On the basis of its amino-acid sequence, prestin (SLC26A5) belongs to the solute carrier 26 family of transporters which exchange halides for SO₄^2- or HCO₃^-. The original electrophysiological analysis of mammalian prestin (Oliver et al. 2001) suggested that such transport functions are minimal; more recent experiments with radioactively labeled substrates also failed to identify a significant HCO₃^- transport (Bai et al. 2009). We have employed sensitive intracellular pH fluorescence probes as an alternative approach to assess the possibility that prestin transports HCO₃^-. A DNA coding sequence of super-ecliptic pHluorin, a pH sensitive variant of GFP, was attached to the C-terminus of prestin and the resulting DNA construct overexpressed in the CHO cell line. As a control for endogenous transport, pHluorin was targeted to the membrane intracellularly using a myristilation-targeting peptide. The experimental data indicate that in the presence of extracellular HCO₃^- the intracellular pH recovers from the CO₂- induced acidification 4 times faster in cells transfected with prestin. This acceleration requires low (4 mM) extracellular Cl^- consistent with prestin transporting HCO₃^- intracellularly in exchange for Cl^-. The process was significantly reduced by extracellular application of 10 mM salicylate, confirming the prestin specificity. As a pHluorin-independent assay, recovery (i.e. HCO₃^- loading) was also only found in those cells expressing prestin using BCECF as a cytoplasmic pH probe. Preliminary quantitative modelling of this system produce pH time courses that mirror the experimental data under reasonable assumptions about the appropriate rate constants. These data therefore suggest that prestin can act as a weak HCO₃^-/ Cl^- antiporter although the effects are anticipated to be greater in OHCs than in expression systems due the higher prestin copy number.