Published data of impact sensitivity of 33 polynitro compounds detected by sound were expressed as the drop energy, E(dr), required for 50 percent initiation probability. A logarithmic relationship has been found between the E(dr) values and heats of fusion of the said compounds. The relationship has been found to be in accordance with the idea concerning the role of plastic deformations of crystal played in the initiation of energetic materials by impact and shock. An analogous application of heats of sublimation has not given convincing results.