An ultrasound pulse transmission technique was studied as an alternative means of measuring the specific interfacial area (a) in gas-liq. reactors. Characterization of gas-liq. dispersions using ultrasound can be a very valuable alternative in situations in which traditional techniques such as those based on optical principles cannot be applied. In order to calc. a from the measured pulse amplitude attenuation, sound scattering theory together with a correction procedure was applied. The ultrasonic pulse transmission measurement was used together with the classical light transmission method in order to measure specific interfacial areas of ?350 m-1 in a bubble column. The results of the 2 methods agreed well. [on SciFinder (R)]