Models have been developed to estimate forest phytomass fractions of major forest-forming species in Estonia, Latvia, Lithuania, Belarus, Ukraine, Moldova, Georgia, Armenia and Azerbaijan. In the development of these models, both specifically collected data (284 sample plots) and some selected data reported in other publications (229 sample plots) were used. The species analysed were pine, spruce, oak, beech, birch, aspen and alder; together these species cover some 92% of the total forested area and growing stock in the countries studied. The models developed include the ratio between the fractions of phytomass weights (dry matter) and green growing stock (stemwood over bark) distributed over age and site indices. The phytomass fractions studied are foliage, wood and bark of the stem; wood and bark of the crown branches: belowground woody phytomass; and understory phytomass. Based on 1988 Forest Stale Account data of the former U.S.S.R., the total phytomass in forested areas (26.3 million ha with a growing stock of 3.85 billion m(3)) was estimated to be 2999.6 Tg (teragrams) dry matter, which gives a phytomass density of 11.4 kg/m(2). The total carbon storage was estimated at 1487 Tg, or 5.6 kg C/m(2). Application of the results from the phytomass studies to the 1966 and 1988 Forest Stare Account data sets results in a net annual average;ink of 24.5 Tg C in the living phytomass of the forest ecosystems in the countries under study over the period 1966-1988. Copyright (C) 1996 published by Elsevier Science Ltd.