Six experiments with sweet potatoes were located on two soil types of the State of São Paulo to study the effects of fertilizer mixtures prepared with different, N. P, and K sources, but containing always 60-100-40 kilograms of N-P(2)0(5)-K(2)0 per hectare. The yield increases of fertilized over the unfertilized plots were satisfactory only in a few of the 11 annual results obtained. Under such poor conditions, superphosphate was slightly superior to bone meal and no difference was observed between coffee ashes and potassium chloride. Ammonium sulphate, in one, and cottonseed meal, in the other five trials, as a rule, were more efficient than Chilean nitrate. Individually, the mixtures prepared with superphosphate, potassium chloride, and ammonium sulphate or cottonseed meal gave the best results but even with them the frequency of satisfactory yield increases was very low.