The theory of operation and experimental test results of a microwave instrument for measuring pressure and temperature in liquid sodium are described. At discrete frequencies, the single, all-metal, hollow cylindrical sensor absorbs energy provided by a wide-bandwidth sweep-frequency microwave oscillator. For the designed sensor, the frequencies of two detected absorption signals relate to temperature whereas the difference frequency relates to pressure. Operational characteristics of the sensor and associated instrumentation were determined over a temperature range of 350 to 1100°F and over a pressure range from atmospheric to 190 psia. Time response of the unit for pressure transients was also ascertained. Total duration of the test approximated 350 hours.