The results of measurement of the Henry's law constant are reported for solutions of H-2 in H2O, with dissolved lithium and boron, at high temperature (220 to similar to 300 degrees C). The experimental procedure involved the use of a palladium/hydrogen electrical resistance sensor to determine the hydrogen gas pressure in equilibrium with the hydrogen dissolved in the water. Values of K-H(infinity) for the above solutions were lower than values for the solute-free H-2/H2O solutions. For conditions typical of a Pressurized Water Reactor (PWR) the lowering amounted to about 3%.