Four trials comparing six phosphorus fertilizers for the production of corn (Zea mays L.) were conducted in 1962-63 at different localities of the State of São Paulo. Practically no effect of phosphorus was observed in one of the trials. As an average of the other three experiments and of the six phosphates tested the yield increases due to the doses of 60 and 120 kg/ha of total P2O5 corresponded to 13 and 18 per cent, respectively. The average increase due to ordinary superphosphate was 683 kg/ha of grain. Giving the value 100 to this increase, the relative efficiencies of the other phosphates were: thermophosphate, 127; mixture of 2/3 of ordinary superphosphate and 1/3 of Araxá phosphate, 75; Olinda phosphate, 71; Alvorada phosphate, 56; Araxá phosphate, 37. The last three carriers are local rock phosphates.