In evergreen tropical rain forest, growing on a nutrient-poor Oxisol (lateritic soil) near San Carlos de Rio Negro, Venezuela, the average total above-ground dry weight of lianas was 15.7 t [tonne] .cntdot. ha-1 which was 4.5% of the estimated above-ground forest biomass. The average leaf area index of lianas was 1.2 m2 .cntdot. m-2 and constituted 19% of total forest leaf area. In comparison to trees, liana stems are small in diameter relative to the sizes of their crowns. This difference in allometry occurs because lianas rely on other plants for support and liana stems generally have large diameter and thus efficient xylem vessels. By maintaining the conducting capacity of their vessels for longer periods of time than do trees, lianas are able to increase further their leaf biomass-stem diamter ratios. Increases in cross sectional areas of liana stems are associated with proportionately larger increases in leaf biomass than comparable increases in cross sectional areas of tree stems.