A structural study of the gum exudate from Enterolobium cyclocarpum has been carried out using chemical methods and 13C NMR spectroscopy. The results reveal that the structure of this gum is essentially a beta-(1-->3)-galactan. Some galactoses are 6-O-linked and others also occur as terminal residues. There is evidence that supports the presence of alpha-L-arabinofuranose and beta-L-arabinopyranose. beta-D-Glucuronic acid may be present as terminal and internal residues, while the 4-O-methyl-alpha-D-glucuronic acid residues exist predominantly in internal positions.