An ultrasonic technique is being developed to detect the dispersed phase holdups in multiphase systems. This technique is based on the fact that the transmission time and attenuation of ultrasound in suspensions differ from those in pure liquids. Experiments were carried out at three probe gap spacing, ( 2.04, 4.27, and 6.31 cm) in a fluidized bed of 7.6 cm diameter. Water was used as the continuous phase and air and 500 mu m glass beads as the dispersed phases. The time-averaged amplitude ratio decays exponentially with gas and solid holdups, whereas the transmission time increases slightly with gas holdup but decreases with solid holdup. It is also observed, for the first time, that the fluctuations of the instantaneous ultrasonic signals can be correlated with the solid and gas holdups in a multiphase system. This correlation may provide a basis for the development of a new approach for phase holdup analysis in multiphase flow systems.