Solute composition of root xylem sap of common native hosts of quandong (Santalum acuminatum) was compared with that of-corresponding xylem sap and ethanolic extracts of endophytic tissues of haustoria of the hemiparasite. Each holt transported a characteristic set of organic nitrogenous Solutes, but little or no nitrate, and the data indicated only limited direct flow of amino compounds between xylem streams of hosts and parasite. Proline predominated in the haustorium and xylem of Santalum, but was at negligible levels in the xylem of most hosts. Sucrose, fructose, glucose, malate and citrate were at high levels in all saps, and fructose especially prominent in Santalum. Chloride, sulphate and phosphate were the principal inorganic anions of the xylem. Based on C:N ratios of xylem and dry matter of Santalum and assuming a 70 % or mere dependence on the host for N, it was estimated that Santalum would gain approximately one third of its C requirement for dry matter production heterotrophically from the xylem of its hosts. Infiltration of xy]em of haustoria-bearing root segments of a major ''nest (Acacia rostellifera) with a range of N-15 labelled substrates resulted in 40-80 % of the N-15 of endophytes of the attached haustoria being received as proline. Nitrate reductase activity was induced in haustoria following host xylem feeding of nitrate. The study concludes that haustoria of Santalum act as a major site of synthesis and export of proline and might therefore play an important role in osmotic adjustment of the parasite and its related acquisition of water from hosts. (C) 1997 Annals of Botany Company.