The variation of net electric charge with pH at four electrolyte concentrations has been determined on samples from four horizons of a krasnozem soil in north Queensland. A potentiometric titration technique was employed, which allowed the estimation of the zero point of charge (zpc) for each sample. Variation in zpc was related to organic matter content and clay mineralogical composition. The charge distribution characteristics explain the amounts of water dispersible clay and phosphate extractable sulphate in this soil.