In the light of putatively increasing liana abundances in present-day tropical forests and a persistent lack of understanding of liana abundance patterns and the responsible factors we attempt to identify the key factors controlling liana abundance along an altitudinal transect in NE Ecuador. At four elevational levels (500 1000 1500 and 2000 m) each represented by 10 plots of 400 m2 the abundance and diameters of all lianas (dbh ‚â• 1 cm) and trees (dbh ‚â• 10 cm) were recorded in old-growth forest stands in the Sumaco Biosphere Reserve (SBR). Results were analysed with available data on soil chemical properties and canopy structure. The mean density of lianas and liana basal area did not differ significantly between the elevational levels; however the mean liana diameter decreased with increasing elevation. Liana density basal area and abundance per tree individual were strongly correlated with host tree diameter. The most important determinants of liana abundance in the SBR were structural stand properties (tree basal area and mean tree dbh) but soil nitrogen availability (indicated by C/N ratio) was also found to have some influence. The notably high variation in liana abundance among different old-growth forest stands mainly reflects differences in stand structure between the studied mature forests whereas the effect of elevation seems to be of less importance.