Effects of ultrasound on the growth and vacuolar H + -ATPase (V-ATPase) activity of aloe arborescens callus cells were investigated. The callus cells cultured in suspension were agitated by an ultrasonic bath at 28 kHz from the exposure time t s =2-60 s, and the cell growth was the highest at t s =5 s as measured by the fresh weight of the callus. The callus cells cultured in solid were exposed by a digital sonifier at 20 kHz in 2 s<t s <10 s with the powers of 1-10 W in continuous wave; at the lower ultrasound powers of 1 and 2 W, the relative growths were increased almost significantly by the exposure from 2 to 10 s. Ultrasound in 10% duty cycle at 20 kHz also enhanced the growth of the solid-cultured aloe callus in 2 s<t s <10 s at 2 W, with no significant differences from the growth in continue wave at 2 W. The V-ATPase activity was detected in tonoplast fractions prepared from the solid callus cultured on agar during 15 days after ultrasound exposures at 2 W both in continuous wave and in 10% duty cycle. In the two exposure modes V-ATPase proton transport and ATP hydrolysis were very similar in their activities increased at 2 and 5 s. Mechanical stress and microstreaming by acoustic cavitation might be considered as the most possible cause of the various physiological effects of ultrasound on the aloe cells. The enhancement of V-ATPase transport and ATP hydrolysis activities seem to be an ultrasound-induced metabolic response of aloe cells.