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Primary production, soil respiration and carbon balance of grazing lands in the semi-arid region of Madurai, India were studied. Heteropogon contortus was the dominant species of the study area and was found in combination with sparsely distributed dicotyledonous species. Primary productivity was estimated by the harvest method, and CO2 emission rates from soil at the study site were measured by the alkali-absorption method. Annual carbon balance was estimated as the difference between input of C via litter and root production and CO2-C output via soil respiration. The total net production of the grazing land was 1618 g/m(2)/yr. The main growth period of the vegetation was the rainy season, live shoot biomass being positively correlated with rainfall. The below-ground contribution to total net production was 36%. CO2 emission rates from the soil during the study period ranged from 65.6 to 183 mg CO2/m(2)/h. Soil respiration was positively correlated (P<0.05) with soil moisture, rainfall and root biomass, and negatively correlated with air temperature. The carbon budget showed that the input of carbon through litter and root production was equivalent to 112.3 and 265.3 g C/m(2)/yr, respectively. The output of organic matter through soil respiration was 309.6 g C/m(2)/yr, which was 82% of total input (377.6 g C/m(2)/yr) in this grassland. The data reveal that 18% of C was accumulated in the detritus system.