The contribution of vines to the evapotranspiration (ET) of a secondary forest in eastern Amazonia was estimated based on field measurements of vine and tree transpiration and seasonal changes in soil water content to 12 meters depth. Transpiration of vines and trees was measured with sapflow gauges placed around stems or branches. Total ET of the secondary forest was estimated as the sum of rainfall and reductions in soil moisture measured using Time Domain Reflectometry sensors installed in the walls of soil shafts. Our results suggest that vines transpire more than trees with stems of similar diameter and with similar leaf crown exposure to sunlight. Trees experienced a smaller reduction in transpiration from the wet to the dry season than did vines. During the dry season vines represented 8% (0.4 mm d(-1)) of total secondary forest ET (5.4 mm d(-1)) but they represented only 5.5% (0.5 m(2) ha(-1)) of total secondary forest basal area (9.6 m(2) ha(-)1). Considering that transpiration corresponds to 66-90% of forest ET vines may contribute 9-12% to the transpiration of the forest. Hence vine cutting which is a commonly recommended management practice to favor the growth of tropical timber trees may result in a proportionally larger reduction in evapotranspiration than in forest basal area.