This paper reports the results of four trials located at Araras, Avaré, Limeira, and São Carlos, in the State of São Paulo, to study the effects of N, P and K on "terra-roxa" soils. The responses to N and K were satisfactory only in the Limeira experiment, located on an area repeatedly fertilized with phosphorus in the previous crops. The small responses to those nutrients in the other localities are attributed to both the low status of phosphorus of their soils and the method of fertilizer application used in the experiments, in the seed furrows, just before planting. Contrarily to the effects of N and K, those of P varied from high to very high in three localities The yield increases due to the applications of 30, 60, and 90 kilograms of P2O5 per hectare corresponded, respectively, to 36, 34, and 42% in Avaré, 36, 39, and 48% in São Carlos, 62, 85, and 96% in Araras, but only to 11, 16, and 12% in Limeira. Here, P showed no effect when applied alone; in the presence of NK, however, its average response reached +18%. The effects of P were also enhanced by the presence of NK in the other experiments. In view of the present results, the authors emphasize the need for revision of the fertilizer program designed to the areas which repeatedly received phosphorus in the previous crops.