Liming recommendations for acid mineral soils based on the neutralization of aluminium have been used since the mid-nineteen-sixties. However, crops vary in their tolerance to Al, the degree of which may be expressed in terms of the percentage Al saturation of the effective cation exchange capacity. Consequently, it is necessary only to apply enough lime to decrease the Al saturation percentage to levels that do not affect production. To facilitate estimation of liming needs, an equation was developed: Mequiv. Ca/100 g soil required for liming = 1.5 [Al – RAS (Al + Ca + Mg) / 100] The value for the elements on the right side of the equation are expressed in terms of mequiv./100 g soil in the original exchange complex of the unlimed soil. RAS = required percentage Al saturation. When the estimated lime requirement is greater than the chemical lime equivalent of the exchangeable Al, replacement of the factor 1·5 with 2·0 gives closer agreement with measured data. The equation can be used to estimate approximate field liming requirements in tons of lime/ha by multiplying the right side of the equation by the apparent specific gravity of the soil. It requires no special soil analysis, only a 1N KCl extraction for the determination of exchangeable Al, Ca and Mg. The use of the equation could lead to considerable savings in the use of lime.