Abstract: Both a method and apparatus for determining internal discontinuities or inhomogeneities in a green or fired ceramic honeycomb structure is provided. In the method of the invention, an ultrasonic transmitter is positioned adjacent to, but not in contact with, the honeycomb structure. The transmitter propagates an ultrasonic wave, of preferably less than 5 MHz, through the honeycomb structure which is received, filtered and analyzed to determine the presence or absence of internal discontinuities or inhomogenieties. The ultrasonic transmitter generates an ultrasonic wave of less than five megahertz to provide a relatively high signal-to-noise ratio in the ultrasonic wave propagated through the structure.