Atmospheric inputs and stream water outputs of P, K,Ca and Mg were estimated for an undisturbed forestedwatershed and the forest ecosystem within it inTaï National Park, Côte d'Ivoire in 1990/91.The study included measurements of wet and drydeposition, and suspended sediments, organic debrisand solutes in the water flows. Base flow as well asquick flow were sampled. The nutrient budgets of theentire watershed and the forest ecosystem (comprisingvegetation and rooted soil layers) were distinguishedon the basis of two assumptions (i) solutes in thebase flow are derived from the soil layers below therooted zone only, and hence not from the forestecosystem; (ii) the total soil mass in the rooted zoneremains constant, i.e. the export of topsoil materialby erosion is compensated for by deepening the rootzone. The first assumption was supported by theresemblance of the molar ratios of solutes in the baseflow and those calculated for the weathering of themigmatite found in the soil layers below the rootedzone. It is concluded that the stocks of P, K, Caand Mg in the watershed are decreasing with 1.4, 12.7,15.3, and 8.1 kg ha-1 yr-1 respectively.Losses are mainly a result of nutrient exports byerosion and solutes in the base flow. Nutrient stocksfor the forest ecosystem are also apparentlydecreasing, but to a much lesser extent, indicatingthe importance of distinguishing between the watershedand the forest ecosystem within.