The enthalpy of sodium paratungstate Na10H2W12O42. 27H(2)O(s) dissolved in solution of 1.0 mol dm(-3) LiClO4 was measured at 298.15 K using a Calvet twin-vessel microcalorimeter. The standard enthalpy of formation of paratungstate B ion, H2W12O4210-(aq), was calculated on the basis of the experimental results. Combining this with values from the literature led to Delta(f)H(m)(0) (H2W12O4210-, aq, 298.15 K)=-(11653.5+/-10.9) kJ mol(-1).