This paper reports the results obtained in five experiments conducted from 1946 to 1950 and designed to study the effect of the addition of cocoa-shell meal to mineral fertilizers supplying 40-120-60 and 80-120-60 kilograms of N-P(2)0(5-)K2O per hectare. The mentioned meal, which is a by-product of the cocoa industry and consists essentially of the shells of the cocoa beans, was applied at rates varying from 255 to 1,100 kilograms per hectare. Two of the experiments were located at Tupi Paulista and the other three at Mococa, State of São Paulo. On the average, in the Tupj experiments the addition of cocoa-shell meal reduced slightly the potato yields, the reduction being greater in the presence of the fertilizer containing the smaller quantity of nitrogen; at Mococa it increased appreciably the yield in the presence of 80-120-60, but was ineffective when added to 40 120-60. Apparently these results indicate that, during its decomposition, the cocoa-shell meal depressed the available nitrogen of the soil. To study the advantage of its addition as organic supplement to mineral fertizers, the cocoa-shell meal should be applied some time in advance of planting; for the aplication immediately before planting, as in the experiments reported, it should be previously composted.