Four experiments comparing six phosphate fertilizers for the production of corn were conducted in 1961-62 at different localities of the State of São Paulo. As an average of the four trials and the six phosphates, the yield increases due to the doses of 60 and 120 kg/ha of total P2O5 corresponded to 24 and 35 per cent, respectively. The average increase due to ordinary superphosphate was 1030 kg/ha of grain. Giving the value 100 to this increase, the relative efficiencies of the other phosphates were: triple superphosphate, 98; dicalcium phosphate, 71; "Alvorada" phosphate, 51; "Olinda" phosphate, 50; "Araxá" phosphate, 40; The last three phosphorus sources are local rock phosphates.