The sonoluminescence emission and sonochemical efficiency of a typical laboratory scale, high-frequency standing wave reactor (355 kHz), stimulated by low-frequency pulses (20 kHz) has been investigated in the presence and absence of some water-soluble solutes, namely, propanol and polyethylene oxide. It has been found that, although dual-frequency sonication causes a decrease in the integrated sonoluminescence intensity and sonochemical efficiency in water, in the presence of solutes, a significant enhancement in activity could be attained. This enhancement effect is ascribed, in part, to changes in the extent of bubble coalescence brought about by the water-soluble solutes.