Abstrucr-A method is described by which the real and imaginary parts of the materials coefficients governing the behavior of a resonator may be found from only three measurements of the immitance. An initial guess of the elastic constant provides a means for the reduction of the immittance formula to an equation, linear in the dielectric and the square. of the piezoelectric constant. Measurement of immittance at two frequencies generates a solvable system of equations. When the dielectric and piezoelectric constants have been found, they can be used for a more accurate determination of the elastic constant, which may replace the initial guess in an iteration procedure. For a complete determination of all materials coefficients, the number of required resonator geometries is shown to be four.