Input-output fluxes of nitrogen (N) and other ecosystem data from 77 forest ecosystems (17 deciduous and 60 coniferous sites) over Europe have been compiled in a database ('Element Cycling and Output-fluxes in Forest Ecosystems in Europe' - ECOFEE) (Gundersen, 1995). The emphasis in ECOFEE is on plot-scale studies in mature stands, including plots within studied catchments, since possible relationships between N fluxes and ecosystem characteristics will be most pronounced on a plot scale. The sites included were investigated for a minimum of 2 years in the period 1985 to 1995. Average N fluxes in bulk precipitation, throughfall, litterfall, leachate below the root zone (output) and N concentrations in various compartments were included along with general site and stand characteristics. The quality of data on output fluxes may be variable between sites since different methods (hydrological modelling, Cl-budgets, or stream runoff) have been used to estimate the output water flux in the original investigations. Forest floor C/N ratios (only available for 33 sites) were if specified calculated from C and N pools in the Ol, Of and Oh horizons (the whole organic layer without freshly fallen litter).