Effects of N and K application on cotton yield, obtained in twenty nine field experiments conducted during the period of 1970-73, at São Paulo State, are related and discussed. Nitrogen was applied in the dosis of 0, 50, and 100 kg/ha of N, and potassium in the dosis of 0, 50, 100, and 150 kg/ha of K(2)0. Yield responses to N application was more frequent in the twenty four experiments conducted with IAC 13-1 cotton variety, on Latosolic B "Terra Roxa", Ortho Dark Red Latosol and Textural B "Terra Roxa". Soil disponibility of P and K, and other factores influenced the effect of N. Yield responses to K+manuring was correlated with the amounts of exchangeable Ca2+ + Mg2+ and K+ in the soil. Also in the five experiments conducted with IAC RM3 variety on podzolized soils, on calcareous sandstone - Marilia and Lins variations, and on Dark Red Latosol phase, the yield responses were more frequent to N application. The effect cf K was not clearly associated with the indices of chemical analyses of the soils.