The effects of ultrasonic treatment on the microbial hydyoxylation transformation of steroid substrate were investigated. Ultrasonic irradiation with comparatively low power and low frequency displayed its notable capability of handling a higher content of steroid substrate for biotransformation. Its function may mainly come from two sides

one is its mechanical action to make the solid substrate finer by interat-trition of those suspended particles

the other is due to its cavitation effect to facilitate easier passage of the fine substrate through the cellular membrane.