A technique for the determination of certain soluble species in solution by the changes they produce in the speed of propagation of ultrasonic waves in the solution was applied to measure the alcohol and soluble solids levels of mouthwashes. The simultaneous determination of these two quantities is made possible by measuring the wave velocity at two different temperatures. The method gives accurate, precise results for the general range of mouthwash compositions in use with appropriate calibration. The advantages of this method over other current methods are precision, speed, and convenience. It is not a suitable regulatory method, however, because calibration must be done with known variations of the particular mouthwash composition to be analyzed.