Thirty six soil samples from various soil series of the County of Piracicaba, State of São Paulo (Brazil), were analysed in order to know the permanent charge of the soil colloidal material. Determination of pH was made in soil suspensions prepared with 10 g of soil and 25 ml of distilled water and with 10 g of soil and 25 ml of 1 N KCl solution. Exchangeable aluminum, hydrogen and calcium plus magnesium were extracted with 1 N KCl solution. Aluminum was determined by the "aluminon" colorimetric method and calcium plus magnesium was determined by EDTA titration. Exchangeable calcium, magnesium and potassium were also extracted with 0,05 N HNO3. Potassium was determined by a flame photometer. The covalently bonded hydrogen was extracted with 1 N calcium acetate solution (pH = 7,0) and its determination was performed by titration with 0.02 N NaOH solution, using phenolphthalein as indicator. The permanent negative charge of the studied soils is very low and a very large proportion is neutralized by aluminum in podzolic soils. The 1 N KCl and 0.05 N HNO3 solutions extracted the same amount of calcium plus magnesium indicating the absence of calcium and magnesium silicate and carbonate minerals in the studied soils. The relationship between pH of the soil water suspension is correlated with base saturation in the KC1 system (r = 0.75 and t = 6.58) and is correlated also with the base saturation in the calcium acetate system (r = 0.87 and t = 10.81). The exchangeable aluminum is correlated with the pH determined in soil-water suspension (r = 0.70 and t = 6.40) and with the pH determined in soil 1 N KCl solution suspension (r = 0.81 and t = 6.40). Finally the pH determined in soil water-suspension is correlated to the hydrogen extracted with 1 N calcium solution pH = 7.0 (r = 0.74 and t = 6.43).