The relationship between storage temperature, relative humidity and seed water content was investigated for four species native to Western Australia: Acacia bivenosa DC., Anigozanthos manglesii D. Don., Banksia ashbyi E. G. Baker and Mesomelaena tetragona (R. Br.) Benth. Water sorption isotherms were constructed at 5, 23 and 50degreesC and the enthalpy of water sorption was calculated by van't Hoff analysis. Seeds of three species, A. manglesii, B. ashbyi and M. tetragona, showed a sigmoidal relationship between seed water content and relative humidity. Intact seeds of Acacia bivenosa maintained a constant water content at temperatures of 23degreesC or less due to the impermeable seed coat; however, isotherms of scarified seeds were similar in shape to those of the other species at all temperatures. The enthalpy of water sorption ranged from -19 kJ mol(-1) for M. tetragona seeds to -29 kJ mol(-1) for B. ashbyi seeds and was dependent on water content. However, all species had a maximum sorption strength at 2-6% water content and three regions of water-binding strength were evident. Each of these species has water sorption characteristics consistent with orthodox storage behaviour and the results of this study provide a framework for improving seed storage methods for the highly diverse Western Australian flora.