In order to test the hypothesis that slowly activating vacuolar (SV) channels mediate Ca^2+^‐induced Ca^2+^ release the voltage‐ and Ca^2+^‐dependence of these K^+^ and Ca^2+^‐ permeable channels were studied in a quantitative manner. The patch‐clamp technique was applied to barley (Hordeum vulgare L.) mesophyll vacuoles in the whole vacuole and vacuolar‐free patch configuration. Under symmetrical ionic conditions the current‐voltage relationship of the open SV channel was characterized by a pronounced inward rectification. The single channel current amplitude was not affected by changes in cytosolic Ca^2+^ whereas an increase in vacuolar Ca^2+^ decreased the unitary current in a voltage‐dependent manner. The SV channel open‐probability increased with positive potentials and elevated cytosolic Ca^2+^, but not with elevated cytosolic Mg^2+^. An increase of cytosolic Ca^2+^ shifted the half‐activation potential to more negative voltages, whereas an increase of vacuolar Ca^2+^ shifted the half‐activation potential to more positive voltages. At physiological vacuolar Ca^2+^ activities (50 μM to 2 mM) changes in cytosolic Ca^2+^ (5 μM to 2 mM) revealed an exponential dependence of the SV channel open‐probability on the electrochemical potential gradient for Ca^2+^ (Δμ~Ca~). At the Ca^2+^ equilibrium potential (Δμ~Ca~ = 0) the open‐probability was as low as 0.4%. Higher open‐probabilities required net Ca^2+^ motive forces which would drive Ca^2+^ influx into the vacuole. Under conditions favouring Ca^2+^ release from the vacuole, however, the open‐probability further decreased. Based on quantitative analysis, it was concluded that the SV channel is not suited for Ca^2+^‐induced Ca^2+^ release from the vacuole.