Soil microorganisms are fundamental to the sustainability of terrestrial ecosystems, especially in soils of medium and low fertility, as is the case in the Amazon. These organisms are important in the transformation of organic matter into nutrients for the soil. Microorganisms also influence the physical conditioning of the soil and the evolution of C02 to the atmosphere. The present work aims to determine the occurrence of microorganisms (fungi and bacteria) in the soil of the Experiment of Drought in the Forest (ESECIAFOR), in the Scientific Station Ferreira Penna, Caxiuanã/PA. The two plots demarcated by ESECLAFOR (A and B) were used to collect the material. Plot B will be used for the water exclusion experiment. Plot A will be used as an experimental control. The soil where the LBA Micrometeorological and C02 Flow Observation Tower (T) is located was also sampled. The soils are classified as Yellow Latosol, ranging from loamy sandy loam and well drained (A and B) to loamy clay loam and moderately drained (T). Composite samples were collected (at depths of 0-5.5-10, 10-25, and 25-50 in) in early November 2001, when there is still a water deficit in the region, and just before water exclusion in plot B. After collection, the samples were refrigerated at 4 0 Caté the shipment to the laboratory. Successive dilutions and "pour plate" plating were performed for microbiological evaluation. Microbial quantification, still in progress, is being determined by counting colonies of fungi and bacteria. Initial results show that there is a difference in the range of occurrence of microorganisms within the same plot. The behavior of fungi was quite different from that of bacteria. Plot B (sandy loam texture and well drained), with relatively low moisture content in the first depths, presented a higher occurrence of fungus at depths from 0 to 25 cm, and at depths from 25 to 50 cm there was a predominance of bacteria
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