Four experiments were conducted in different parts of the State of São Paulo to study the effect of increasing doses of nitrogen, phosphorus and potassium on the yield of sweet potatoes. Nitrogen and potassium did not increase significantly the yields in any of the experiments. Also no effect of phosphorus was obtained in two of them - one localized on fertile soil and the other on soil fertilized with that element in the previous crops. However, in the two experiments conducted on areas not fertilized in the previous years, the increases due to 60 and 120 kg/ha of P2O5 were highly significant and linear.