The enthalpies of solution of five hydrated calcium berates in approximately 1 mol.dm(-3) aqueous hydrochloric acid were determined. From a combination of these results with measured enthalpies of solution of H3BO3 in HCl(aq) and of CaO in (hydrochloric acid + boric acid) (ag), together with the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(1), the standard molar enthalpies of formation of the five hydrated calcium berates were obtained.