The experimental data available on the standard enthalpy of formation DELTA(f)H(theta) of crystalline solvates containing H2O, CH3OH, C2H5OH, H2O2 or SO2 have been evaluated using the equation DELTAPHI = DELTA(f)H(theta)(M(a)X(b) . nY) - DELTA(f)H(theta)(M(a)X(b)) = b(n)n. This equation presents satisfactorily the data available on DELTA(f)H(theta) for the above solvates. The unknown values of DELTA(f)H(theta) for some crystalline solvates and unsolvated salts are predicted.