Water and nutrient fluxes in a Nathofagus pumilio forest, located in the Puyehue National Park (41 degrees S, 72 degrees W, 1120 m a.m.s.l.), during a 18-month period (July 1997-December 1998) were studied. Measurements of precipitation, throughfall, stemflow, effective precipitation, soil water infiltration and runoff were carried out in an experimental microcatchment. Simultaneously, monthly water samples were collected to determine the concentrations and fluxes of NO3-N, NH4-N, total-P, K+, Na+, Ca2+ and Mg2+. During 1997, precipitation was 5332 mm (78% as rain and 22% as snow). Throughfall was 4701 mm, stemflow 481 mm and runoff 4234 mm. The average pH of precipitation, throughfall, stemflow and effective precipitation was 5.7, increasing their value in soil water infiltration (pH = 5.9) and runoff (pH = 7.0). The water in the forest was rich in cations, specially the runoff where K+, Na+, Ca+ and Mg2+ concentrations were higher than those in the precipitation. NO3-N concentrations were higher in the forest, but lower in the runoff. However, NH3-N concentrations were lower in all levels of the forest in relation to precipitation. The total-P concentrations were higher in all levels of the forest, compared to precipitation. The input of inorganic nitrogen via precipitation was 3.3 kg ha(-1) yr(-1) (NO3-N = 1.3 and NH4-N = 2.0 kg ha (-1) yr (-1)), and the output via runoff was 0.66 kg ha(-1) yr(-1) (NO3-N = NH4-N = 0.31 kg ha(-1) yr(-1)), therefore the nitrate and ammonium retention efficiency were 72% and 85%, respectively.