Ten experiments were carried out in 1961-62 and 1962-63 at eight different localities of the State of São Paulo to study methods of nitrogen (ammonium sulfate) application to corn. Besides one treatment with PK and one with NPK, in which the fertilizers were side-placed at planting time, four further treatments were included to study the effect of supplementary amounts of nitrogen applied as top-dressing. In two of the latter treatments nitrogen was applied eight inches from each row; in the other two, in the center of the odd inter-rows. In each type of localization the top-dressed amount of nitrogen was applied either 45 days after planting or halved for applying 30 and 60 days after planting. The following rates of nitrogen were used: at planting time, 30 kilograms to the hectare in 1961-62 and 20 in 1962-63; as top-dressing, 90 and 100 kilograms, respectively. Nitrogen did not increase the yields in two of the ten experiments and no difference was observed between the methods of top-dressing in the remaining eight experiments. Applied exclusively at planting time, nitrogen favored the growth of the plants but only in two experiments it increased the yields. However, when applied both at planting time and as top-dressing, it increased the yields in all of the eight experiments, its average response being +1,021 kilograms to the hectare, corresponding to +27% of the PK treatment yield.