As a contribution to the knowledge of the residual effect of phosphorus fertilizers applied to the soils of the State of São Paulo the authors report the results obtained in two experiments with corn, one conducted on "terra-roxa-misturada" soil, in Campinas, and the other on sandy soil of the glacial type, in Ipanema. In both experiments the effect in question was very high. In Campinas the residual effect of superphosphate was equal, but in Ipanema it was superior to that of other relatively insoluble phosphates. The authors reviewed also the results of various other experiments conducted in the State of São Paulo and concluded that it is impossible up to now to establish, for each type of soil, numerical relations between the residual effects of the phosphates studied. They state, however, that even in the red soils or in the "terra-roxa" the residual effects of superphosphate, as well as that of the other phosphates ordinarily used in São Paulo, are generally high enough to permit the reduction of the quantity of phosphorus to be applied on soils fertilized with this nutrient in the previous crops. Finally they point out the need of more detailed investigations to study the degree of reduction to be applied in every case.