A field experiment (Pindomonhangaba Exp. Sta.) and greenhouse test (Instituto Agronômico) were carried out to study the phosphorus availability of three Brazilian rock phosphates under different conditions of soil acidity. The soil on which the field experiment was conducted was classified as "série monotipica Pinda". Samples from the same soil were used for the greenhouse test. Araxá phosphote. Olinda phosphote. Alvorada phosphate (apatita do Morro do Serrote), and ordinary superphosphate were utilized as phosphate sources. Corn hybrid (HMD - 6999) was used as an indicator plant. Twelve treatments were compared in the field experiment in a randomized block design with three replications. They were os follows: (1) NK; (2) NK + 1/2 lime; (3) NK + lime; (4) NK + superphosphate; (5) NK + superphosphate + 1/2 lime; (6) NK + superphosphate + lime; (7) NK + Olinda; (8) NK + Olinda + 1/2 lime; (9) NK + Olinda + lime; (10) NK + Araxá; (11) NK + Araxá + 1/2 lime; (12) NK + Araxá + lime. The results from the field experiment were measured as grain yields. In the pot experiment, the same twelve treatments as mentioned above plus N0P0K0 and NK + Alvorada in presence of three doses of lime (0, 1/2 and 1) were included. The pH of soil from the pots of all treatmens was checked before sowing. The results were meosured as dry matter weight of aerial parts of the plants, harvested five days after the male inflorescence started to blossom. Determinations of CaO, MgO, and P2O5, were made. The results from the field experiment indicated that the soil pH had no influence on the phosphorus availability of the rock phosphates tested. This fact might have been due to liberation of soil organic phosphorus, which may have masked the soil acidity effect. In the pot experiment, however, the results indicated that the effect of the soil pH varied according to the type of rock phosphate. The Alvorada phosphate was less available when the soil pH was increased by liming, and this effect was reflected on the weight of the plants. The Olinda and Araxá phosphates increased mass production when the highest rates of lime were applied.