Seed glactomannans function as both an energy reserve and a water reservoir in germinating seed of many leguminous plants, and are used commercially as gelling agents, mainly in processed foods. Cassia brewsteri is a leguminous tree endemic to eastern Queensland. The galactomannan content of 40 samples of C. brewsteri seed from throughout the distribution of the species ranged from 28.3 to 39.7% of seed dry weight. The galactomannan content of whole seed was 33.7 +- 0.4% (mean and s.e.m.on a dry weight basis). The mannose: galactose ratio ranged from 4.6 tp 6.3 and averaged 5.4 +- 0.1. C. brewsteri gums prepared in a manner analogous to that used in the preparation of commercially available carob gum were tested for gel strength relative to industrial gelling agents carob gum and Senna tora gum. The break force index (BFI) for the most effective C. brewsteri gum preparation was 107% relative to carob gum and 83% relative to Senna tora gum. On the basisof these biochemical and fundamental data, C. brewsteri has potential as a source of commercial seed galactomannas.