A knowledge of the chemical characteristics of tropical and subtropical soils, is essential for the development of our agriculture. In the present study examinations were made on samples of the four principal soil types of the State of São Paulo. These types are ; Massapé-salmourão, Glacial, Terra-roxa legítima and Arenito Bauru. Determinations were made of the proportional amounts of the mineral elements potassium, calcium and magnesium, that were in exchangeable and nonexchangeable forms. A description is given of the physical-chemical and mechanical properties of the soils samples and data are presented on the amounts of "exchangeable" potassium, calcium and magnesium, obtained from the samples by two different chemical methods. In one method of extraction normal solution of amonium acetate was used and in the other a 0.05 N solution of nitric acid was employed and the results obtained from both methods of extraction were very similar. The same samples that were treated with the 0.05 N nitric acid for determination of the "exchangeable" elements, were subsequently treated with 5N HCl solution in order to determine if there was still present K, Ca and Mg cations in a "fixed form". It was found that the amount of calcium extracted by the 5N HCl solution was very small but that the amounts of potassium and magnesium were high. This indicates that the calcium was present almost entirely in an exchangeable form, in the samples tested, whereas the potassium and magnesium were present not only in an exchangeable form but also in a fixed form.