Piezoelectric data on a mixed titanate system (82.0%BaTiO3, 9.1%CaTiO3, 3.6%PbTiO3, and 4.4%TiO2were obtained with an apparatus intended to measure the dynamic compressibility of materials. The calibration constant, determined from measurements on specimens of known compressibility, involves the piezoelectric and dielectric constants of the ceramics used as transducers. The method is discussed and an operating equation for the apparatus derived. Piezoelectric and dielectric constants have been measured as a function of temperature and pressure over the ranges: −25 to 37.5°C and 0 to 1000 kg/cm2. An apparant phase transition was observed near 5°C. A qualitative discussion of the results is given.