The problems connected with soil testing on calcareous soils are discussed. It is pointed out that in calcareous soils pH differences in the range of pH 7.0–8.5 are meaningless unless the measurements are made under standard conditions with respect to CO2 and Ca-ion concentration. A knowledge of CO2 variations under field conditions is considered essential for proper ecological interpretation of the reaction of calcareous soils. It is stressed that the lime fraction in calcareous soils has its own inherent particle size distribution. Information regarding this fraction should therefore be included in the mechanical analysis of the soils. A method for the determination of the size frequency distribution of the CaCO3 is outlined. A simple method for the determination of the reactivity of the lime is described and the various conditions affecting the reaction are discussed. The method gives the relative surface area of the lime by oxalate adsorption and is used for the diagnosis of susceptibility to lime-induced chlorosis.