Aluminum concentrations, fluxes, and storage were measured in the vegetation, forest floor, and acid, sandy mineral soil of a forested watershed in the New Jersey Pine Barrens. Volume-weighted mean Al concentrations in solution increased as water passed through the upland ecosystem, from 0.012 mg/l in bulk precipitation to 0.14 mg/l in throughfall to 0.45 mg/l in E horizon mineral soil, 0.60 mg/l in the B horizon, and 0.73 mg/l in the C horizon. Weighted mean Al concentration of the stream water was 0.15 mg/l. Solution Al concentrations in different compartments of the ecosystem were related to the magnitude of moisture flux, dissolved organic carbon concentration, and pH. Soil solution and stream water Al concentration were high in the winter and spring and low in the summer and fall, inversely following solution pH.