The construction of semiquant. energy/temp. (E/T) diagrams is discussed on the basis of thermodn. equations. An E/T diagram describes the temp. dependence of the enthalpy and the Gibbs free energy of polymorphs. Knowledge of the E/T diagram of a compd. permits the prediction of relative physicochem. values for polymorphs. Construction and interpretation of E/T diagrams is discussed with ref. to the drugs, nimodipine and acemethacin. The predicted data are compared with exptl. values.