The phytomass structure of the evergreen lowland forest vegetation (Tall Amazon Caatinga) supported by tropaquods near San Carlos de Rio Negro, Federal Amazon Territory of Venezuela was studied in 13 10 m X 10 m plots. The plots were laid out subjectively to cover a low topographical gradient along which the forest on tropaquod is grading into a low woodland (Bana, or Low Amazon Caatinga). The phytomass was estimated by destructive sampling.The total living phytomass (dry matter) varies between I99 t/ha in one plot including a natural gap, to 822 t/ha in a plot located near a blackwater creek draining the 10 ha study site in which the vegetation was surveyed. Dead aboveground phytomass (dry matter) varies between 2 and 37 t/ha. The average leaf area index is 5. t. Leaves are sclerophyllous. The mesophyll leaf size class is dominant.Compared with other Amazonian rainforests the Tall Amazon Caatinga is lower in aboveground phytomass and wood volume, respectively, but its root average proportion is 2.4 times greater.One hundred and thirty species (dbh 1>1 cm) were recorded in all plots, 14--45 species per plot composed the aboveground phytomass. 20 species each had a relative frequency of 50 or more percent. 7 of these species plus 10 less frequent ones each represented 10 or more percent of the basal area in at least 1 plot. Sixteen species each contributed l0 or more percent to the aboveground phytomass, in at least 1 plot. There is only 1 species (Micranda sprucei, Euphorbiaceae) which was observed in all plots. Its contribution to basal area and aboveground phytomass is considerable. M. sprucei is also the dominant species of the top canopy layer.