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The purpose of this work was to verify soil respiration kinetics in two sites in the semi-arid region of Paraiba, Northeast of Brazil. The first was a Mimosa hostilis Benth (jurema preta) colonized site, and the other was a degraded area without vegetation. Soil respiration was estimated every hour during a period of 12 hrs. Absorption of the liberated soil CO2 was obtained using a KOH 0.5 N solution. The amount of absorbed CO2 was determined through titration with a HCl 0.1 N solution. Temperature was measured at the surface and 10 cm deep in the soil in both areas. It was observed that the highest level of microbial activity, at the jurema preta site, occurred from 10:00 to 12:00 o’clock AM. The lowest level of microbial activity was observed when temperature reached 50 degrees C. In the degraded area, microbial activity reached a maximum at 14: 00 o’clock PM due to the reduction of soil temperature.