The interpretation of the most interesting analitical data of the soils of the State of São Paulo is presented. The work is based on the study of nearly 1800 analyses of 450 typical profils and 1350 superficial samples of soils. The analitical methods here employed are described. Determinations have been made of exchangeable K, Ca, Mg, Mn and PO4; T - S, total C and total N. Since the exchangeable capacity of bases represents both, an essential chemical characteristic of soils and their colloidal properties, a great significances is atributed to it. Other considerations on the exchangeable ions are made, showing its value as a propor character of the soil, independent in limited way, of the conventional extraction concepts.