Upon cooling and compression, both the thermodynamic and the kinetic properties of glassformers change. In fragile glassformers, these changes suggest changes in the local structure of the liquid. Thermodynamic data may then provide a measure of structure changes. Special criteria for structure changes in terms of energy and pressure fluctuations in the isochoric system are proposed; recent theoretical results allow one to rewrite the criteria in terms of long- and short-time thermodynamic characteristics of the liquid. Based on the proposed criteria, we discuss the changes in the local structure due to temperature and pressure variations. (C) 2004 American Institute of Physics.