An experimental study has been carried out to determine the effect of solution composition on the partitioning behaviour of tungsten in granitic melt-vapour systems at 800° C and 1 kbar. With chloride and phosphate solutions, tungsten partitions strongly into the aqueous phase, whereas with fluoride, carbonate and borate solutions, and water alone, tungsten partitions in favour of the melt. With chloride solutions, the fluid/melt partition coefficients (K _D) for W show a marked positive correlation with chloride concentration, and suggest that at low chloride concentrations W-Cl complexes with low Cl∶W ratios (such as associated equivalents of (WO₃)₂C1⁻) may be present. In contrast, at higher chloride concentrations complexes with high Cl∶W ratios (such as WOCl₄, WCl₆ and associated ionic equivalents) may predominate. With phosphate solutions, K _D shows little variation with phosphate concentration, and phosphorus heteropolytungstates (such as H₃[PW₁₂O₄₀]) may be present. There is no evidence to suggest that fluoride, carbonate or borate complexes of tungsten are important under the experimental conditions: the data for these compositions can be interpreted assuming that isopolytungstates (such as H₆[H₂W₁₂O₄₀]) are present. Within high temperature hydrothermal solutions tungsten may be transported principally as isopolytungstates and heteropolytungstates in addition to chloride complexes, and this may, in part, account for the common association of apatite and arsenopyrite with scheelite and wolframite in tungsten deposits.