The effects of changes in the extracellular pH (pH_o) on low-voltage- (LVA) and high-voltage- (HVA) activated calcium currents of acutely isolated relay neurons of the ventrobasal thalamic complex (VB) were examined using the whole cell patch-clamp technique. Modest extracellular alkalinization (pH 7.3 to 7.7) reversibly enlarged LVA calcium currents by 18.6 ± 3.2% (mean ± SE, n = 6), whereas extracellular acidification (pH 7.3 to 6.9) decreased the current by 24.8 ± 3.1% ( n = 9). Normalized current amplitudes ( I/ I _7.3) fitted as a function of pH_o revealed an apparent pK_a of 6.9. Both, half-maximal activation voltage and steady-state inactivation were significantly shifted to more negative voltages by 2–4 mV on extracellular alkalinization and to more positive voltages by 2–3 mV on extracellular acidification, respectively. Recovery from inactivation of LVA calcium currents was not significantly affected by changes in pH_o. In contrast, HVA calcium currents were less sensitive to changes in pH_o. Although extracellular alkalinization increased maximal HVA current by 6.0 ± 2.0% ( n = 7) and extracellular acidification decreased it by 11.9 ± 0.02% ( n = 11), both activation and steady-state inactivation were only marginally affected by the moderate changes in pH_o used in the present study. The results show that calcium currents of thalamic relay neurons exhibit different pH_o sensitivity. Therefore activity-related extracellular pH transients might selectively modulate certain aspects of the electrogenic behavior of thalamic relay neurons.