Abstract The objective of this investigation was to determine the lime requirement of soil by means of electro-ultrafiltration (EUF). Pot experiments with barley using ten acid soils showed that their lime requirement was related to the Ca2+ extracted by EUF and to the quantity of water that flowed through the anode filter during the extraction. This water quantity was correlated with the cation exchange capacity and hence is an indicator of CEC. The regression equation for the lime requirement comprised the variables: Ca2+ extracted, water flow through the anode filter of the first (200 V, 20 °C, 30 min) and the second EUF fraction (400 V, 80 °C, 5 min). It had a coefficient of determination (r2) of 0.993. In a Mitscherlich pot experiment with barley, using six acid soils, lime rates determined according to the EUF method (regression equation) were compared with those lime rates determined by the Schachtschabel method. On average, lime rates determined by the Schachtschabel method were greater than those calculated from the EUF data. Lime application to soils with a pH < 5.0 resulted in significant yield increases, which on average were the same for both methods for determining lime requirement. Of the six soils tested, two responded with higher yields when limed according to the Schachtschabel method than with the EUF method and one, the most acid soil (pH 3.25), gave a higher yield when limed according to the EUF method. At pH levels > 4.7, CaSO4 application gave the same yield response as the application of equivalent amounts of CaO. On one soil, CaSO4 was superior to CaO.