AbstractMature 40-year-old trees of Eucalyptus globulus harvested in Portugal were studied to determine the heartwood development and variation of basic density and extractives content at different stem height levels. The heartwood radius decreased regularly from bottom to top in all the trees: for instance 22.2 cm, 13.0 cm, and 10.4 cm, respectively, at the 0%, 35%, and 60% height levels of tree 1. The average sapwood thickness was 2.8 cm at the stem base. The mean basic density fell in a range between 0.607 g cm-3 and 0.782 g cm-3 and was highest in the outer heartwood at all height levels. The total content of extractives varied axially and radially along the stem. It decreased until the 35% height level, and then it remained approximately constant upwards. The extractives content increased radially from the sapwood to the inner heartwood (6.2% to 12.5% at the base). Ethanol-soluble compounds were the major fraction at the base: 4.9%, 8.4%, and 10.9% of dry mass, respectively, for sapwood, outer heartwood, and inner heartwood. The non-polar extractives were obtained by dichloromethane extraction in very low amounts.