The quantification of carbon stored in the soil-vegetation system is fundamental to study the CO₂ cycle which is closely related to the global warming, topic theme of the Kyoto Protocol. With regard to this issue, the Lombardy Region (Italy) is carrying on studies for the quantification of the organic carbon stored in the soils and in the forest biomass of its territory and is predisposing a database of historical climatic data. The input data (for soils and for vegetation) were taken from ERSAF databases; the unitary organic carbon content was calculated applying the formulas cited in Batjes (1996) for soils and in Susmel (1988) for the vegetable biomass. The total stock was calculated from the unitary data considering the areas covered by soils and forests communities in Lombardy. The total organic carbon content in the Lombardy soil cover (23,855 km²) is 130.232 Mt in the superficial ploughed layer (the upper 30 centimetres) and 276.012 Mt in the entire profile (200 centimetres). The organic carbon content in the forestry biomass was calculated for areas covered by broadleaved and coniferous trees. The calculated total biomass is equal to 122.864 x 10⁶ m³, or, if expressed by weight, 19.75 Mt of organic carbon. Figure 1 illustrates the distribution of the quantitative of organic carbon stored in soil-vegetation system of Lombardy. It can be observed that nearly half of the total organic carbon content of the soil profiles is concentrated in the first 30 cm and that the percentage increases to 85% if the upper 100 cm are considered. This behaviour is particularly evident for Leptosols, Umbrisols and Phaeozems (WRB, 1998), while in other soils organic carbon has a more homogenous distribution with a relatively high content also in the depth layers; this is evident especially for organic soils (Histosols) and, to a lesser extent, in soils with vertic characters (Vertisols and Vertic Cambisols) and in Fluvisols (WRB, 1998). Unitary organic carbon values in the soils and the forest biomass, deduced for the Lombardy, are in close agreement with the results shown from other European and national studies (APAT, 2002). It can be also observed that, for a fixed area, the organic carbon content in soils is 10 times greater that the content in the forest biomass. In conclusion, soils are a relevant terrestrial reservoir of organic carbon; together with forests, they are the key compartments where men can operate to increase the pool of organic carbon. Using the values calculated in the present studies, it can be observed that an increment or a loss of only 1% of the unitary organic carbon contents (kg/m²) in the ploughed layer (upper 30 cm) would increase or decrease the organic carbon content stored in regional soils of nearly 617,000 tons. The conservation and the valorisation of soils and forests are therefore crucial for the implementation of the Kyoto Protocol. Together with programs of reforestation and forest safeguard, a policy aiming to preserve and increase the stock of carbon stored in soils (that could be considered a "tank" of excess atmospheric CO₂) are also fundamental. Bibliography: (1) APAT (2002). Assorbimento e fissazione di carbonio nelle foreste e nei prodotti legnosi in Italia. APAT Rapporti 21/2002, 58 pp. (2)Batjes N.H. (1996). Total carbon and nitrogen in the soils of the World. European Journal of Soil Science, n° 47, pp 151-163. (3) Susmel L. (1988). Principi di ecologia. Fattori ecologici, ecosistemica e applicazioni. Ed. CLUEP, Padova.