The surface potential at the ice-water interface was measured with an ice electrode as a function of pH. Equilibration in the basic region was found to be slow and no stable potential was obtained. In the pH region below 8 the equilibration was fast, yielding stable and accurate values of the surface potential. The effect of Na+, K+ and Mg2+ ions was examined. It was found that these ions do not have a different influence on the surface potential in the entire pH region.