Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of human eosinophils, at various pH_i with pH_o 7.5 or 6.5 pipette solutions. H⁺ current fluctuations were observed consistently when the membrane was depolarized to voltages that activated H⁺ current. At pH_i ≤ 5.5 the variance increased nonmonotonically with depolarization to a maximum near the midpoint of the H⁺ conductance-voltage relationship, g_H-V, and then decreased, supporting the idea that the noise is generated by H⁺ channel gating. Power spectral analysis indicated Lorentzian and 1/f components, both related to H⁺ currents. Unitary H⁺ current amplitude was estimated from stationary or quasi-stationary variance, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{{\sigma}}_{\mathrm{H}}^{\mathrm{2}}\) \end{document}. We analyze \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{{\sigma}}_{\mathrm{H}}^{\mathrm{2}}\) \end{document} data obtained at various voltages on a linearized plot that provides estimates of both unitary conductance and the number of channels in the patch, without requiring knowledge of open probability. The unitary conductance averaged 38 fS at pH_i 6.5, and increased nearly fourfold to 140 fS at pH_i 5.5, but was independent of pH_o. In contrast, the macroscopic g_H was only 1.8-fold larger at pH_i 5.5 than at pH_i 6.5. The maximum H⁺ channel open probability during large depolarizations was 0.75 at pH_i 6.5 and 0.95 at pH_i 5.5. Because the unitary conductance increases at lower pH_i more than the macroscopic g_H, the number of functional channels must decrease. Single H⁺ channel currents were too small to record directly at physiological pH, but at pH_i ≤ 5.5 near V_threshold (the voltage at which g_H turns on), single channel–like current events were observed with amplitudes 7–16 fA.