Some plant species can change soilphosphorus (P) availability and this may be an important tool in managing tropical high fixing phosphorussoils. An experiment was conducted to evaluate phosphorus transformations in the soil and phosphatase activity during periods of Congograss (Brachiaria ruziziensis, Germain et Evrard) growth in two tropical soils receiving 20, 40, 80, 160 mg dm-3 of inorganic P. Plants were grown for 84 days in 8-L pots. Acid phosphatase activity, P in the microbial mass, soil organic and inorganic P and P accumulation by Congograss were evaluated. Phosphorusfertilization increased soil P availability, Congograss yields and P accumulation in the plant. On average, less labile P forms in the soil were not changed by Congograss; however, the P in the soil extracted with HCl (P-Ca - non labil form) decreased. This decrease may have resulted from the combination of the presence of grass and phosphatase capacity to dissolve less available P in the soil. Thus, soil exploration by Congograss roots and the subsequent extraction of calciumphosphate may have increased the P concentration in the planttissue. Despite the decrease in the P extracted from the soil with HCl resulting in increased labile P forms in the soil, the effect of Congograss on the availability of P depends on the soil type.(AU)