Pressure perturbation calorimetry is a rather new technique which serves to measure the temperature-dependent thermal volume expansion of a solute or particle in aqueous dispersion. It can be used to detect thermotropic transitions in lipid systems and to characterize their accompanying volume changes and kinetics. The results are of highest precision and obtained in a very convenient, fully automated experiment, requiring relatively little material. The strategy of the technique is to measure the heat response to a very little, isothermal pressure perturbation in a high-sensitivity isothermal calorimeter. On the basis of such data, thermodynamic laws and considerations yield the thermal expansion of the partial volume of the solute or colloidal particle.