Hydrogen sulfide (H2S) is emerging as an important regulator of ion channels1, which may account for many of this gasotransmitter’s biological actions. The purpose of this study was to investigate its effects on T-type Ca2+ channels. The three different isoforms of T-type Ca2+ channels were separately overexpressed in HEK293 cells. Using patch-clamp electrophysiology, we demonstrated that the H2S donor, NaHS (10µM-1mM) selectively inhibits Cav3.2 T-type channels whilst Cav3.1 and Cav3.3 channels are unaffected. This inhibitory effect is voltage-independent and concentration-dependent: 10µM NaHS was sufficient to evoke a significant reduction of Cav3.2 current, and maximal inhibition (ca. 35%) was observed at 1mM NaHS. Although H2S-dependent inhibition of Cav3.2 persisted (>5 min) after washing NaHS out, the reducing agent dithiothreitol (DTT) immediately reversed this inhibition, suggesting that this mechanism is redox modulated. Mutagenesis studies revealed that the redox-sensitive extracellular residue H1912 was essential for H2S sensitivity: currents evoked in mutant Cav3.2 (H191Q)-expressing cells were insensitive to NaHS, and the analogous reverse mutation in Cav3.1 (Q172H3) conferred sensitivity to NaHS on Cav3.1. We also explored the ability of H2S to inhibit native T-type currents in rat aortic smooth muscle (A7r5), murine atrial cardiomyocytes (HL-1), rodent neuroblastoma x glioma hybrid (NG 108-15) cells, and primary cultures of rat dorsal root ganglia (DRG neurons). H2S inhibition correlated with expression of Cav3.2 and not Cav3.1 channels. Importantly, H2S also inhibited native T-type (primarily Cav3.2) channels in DRG neurons, where inhibitions of ca. 20% were observed. Our data clearly indicate that H2S selectively inhibits Cav3.2 T-type Ca2+ channels in the micromolar concentration range and inhibition requires the presence of H191 (see also J. Elies et al. (2014). FASEB J. 28(12):5376-87). The results obtained from this study raise important issues regarding the mechanisms involved in the biological actions of H2S in health and disease.