The gum exudate from Acacia calcigera, a species recently discovered in Australia, has been shown to have a highly positive specific rotation and high molecular weight with a low rhamnose con­tent. These results are characteristic of species within the Sec­tion Gummiferae, a predominantly African section of the genus Aca- cia. Analytical data for the gum exudate from a cultivar of Leucaena leucocephala from India and for gum arabic (Acacia senega!) fromAfrica were compared. The Leucaena gum had a chemical composition and properties sim ilar to gum arabic but was of higher viscosity and molecular weight; these differences could be commercially important if gum collection from Leucaena could be organised. in a series of studies in laboratory rats, gum arabic was com­pletely degraded on incorporation into a standard rat diet at levels of 2g/day/rat and 4g/day/rat. On incorporation into an elemental, low residue diet ( ‘Flexical1) gum arabic was partially degraded when fed to rats at 2g/day/rat but was found to be degraded more exten­sively if fed at a reduced level (lg/day/rat). Gum arabic, mixed with faeces from rats fed the elemental diet was partially degraded by faecal bacteria. The different results obtained when gum arabic was incorporated into two different diets indicated the importance of choice of type of diet and dose level used in dietary studies. VFaecal extracts obtained from rats fed a standard diet supple­mented with gum karaya (1.2g/day/rat) were shown to be similar, but not identical, to gum karaya that had been mixed with faeces then re-extracted. A similar result was obtained when an elemental diet was used. It was not possible to conclude whether or not the gum karaya extracted from test faeces had been degraded because of the difficulties found to be associated with attempted molecular weight measurements of the impure forms of the gum extracted. Seven commercial gum tragacanth samples from Iran were found to vary in composition and in viscosity and in the ratio of their water-insoluble and water-soluble components. Their amino acid con­tents did not differ extensively. Five commercial gum tragacanth samples from Turkey showed less variation than the Iranian samples; although having lower viscosity, their amino acid compositions were sim ilar to those of the Iranian samples. A Turkish gum tragacanth sample from Astragalus microcephalus (the major source of the gum) differed extensively analytically from Turkish gum tragacanth sam­ples from Astragalus kurdicus and Astragalus gummifer (minor sources) The Test Article used in a dietary study of gum tragacanth in Man was shown to have been well-chosen, representing gum tragacanth of fair average quality.