This paper reports the first 9-year results of an experiment in which the effects of manure, limestone, and a NPK fertilizer are being tested on continuous corn. The experiment is located at Campinas, on a «terra-roxa-misturada» soil fairly fertile with the initial pH of 5.6. The corn yields were generally satisfactory and tended to increase during the indicated period, this being attributed to the accumulation of residues of the successive fertilizer applications and the use of more productive hybrids. The average effect of lime was null, but its interaction with NPK was significant and positive: in the absence and in the presence of NPK respectively, the responses to lime corresponded to -205 and +204 kg/ha (kilograms per hectare). The yield increases due to manure were very good and more or less constant during the period studied. Its interaction with NPK was significant and negative: +1,340 kg/ha in the absence and only +443 kg/ha in the presence of NPK. As to NPK, its effect was significant and tended to increase considerably as the years passed. While the presence of lime enhanced it, that of manure depressed it. In the 9-year average the response to NPK, which reached +1,904 kg/ha in the absence, dropped to +1,007 kg/ha in the presence of manure. However, the yields still increased where NPK + manure were applied. The authors also studied the influence of the treatments on some characteristics of the corn plant and ears, and on the chemical properties of the soil, as well as the most profitable rates of NPK applications.